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Digital Clamp Meter: A more versatile Measuring Instrument

Measurement of Current.. Yeah! the usual meter that comes in mind for current measurement is the ammeter. These meters have to be connec...

Saturday, 11 February 2017

Digital Clamp Meter: A more versatile Measuring Instrument

Measurement of Current..

Yeah! the usual meter that comes in mind for current measurement is the ammeter. These meters have to be connected in the circuit to get the reading. Thus, for current measurement using ammeter, we have to disturb the circuit and put the meter in between. Also the prior knowledge of the magnitude of circuit current and it’s nature is necessary. One should also know the proper method and have the means to disconnect and reconnect the circuit.

Clamp-On ammeter is a very handy device which can measure the current flowing through any LT circuit without disturbing the existing connections.

Clamp meter:

A clamp meter is a more versatile instrument that combines a clamp-on ammeter with a multi-meter. It is usually capable of measuring alternating current, AC/DC voltage, and resistance. Many of these meters are able to test the capacitors, measure frequency, temperature, continuity etc. Continuity is a quick test to check an open circuit. When the circuit is closed, the meter emits a “beep” sound. 

The display can be analog or digital; accordingly are called analog or digital clamp meters. Digital meters have several advantages over analog ones and thus are commonly used. Figure 1 shows a digital AC/DC clamp meter.

Fig.1: A digital AC/DC clamp meter

Clamp meters have a movable jaw that can be opened. Open jaw allows the clamp meter to be clamped around a current carrying wire to measure the current flowing through the circuit. Figure 2 shows the digital clamp meter with open jaws.

Fig.2: Digital clamp meter with open jaws.

Working of DC clamp meter:

Conventional clamp meters, capable of measuring alternating current only, do not show the reading when used to measure DC current. DC clamp meters work on the principle of “Hall Effect”. The magnetic field because of DC current produces a small voltage across the Hall Effect sensor. This voltage, which is proportional to the DC current flow, is further amplified for measurement.

DC clamp meters or AC/DC clamp meters are very useful in Solar PV system installation and maintenance, since the output current of a solar PV plant is DC in nature. 

Accessories such as pair of red and black probes for voltage measurement and thermocouple with leads (clamp meters with temperature measurement facility) are provided. Figure 3 shows the thermocople with leads. Figure 4 shows how the thermocouple leads are connected to the clamp meter (also shows the temperature).

Fig.3: Thermocople with leads

Fig.4: Thermocouple leads connected to the clamp meter

The digital AC/DC clamp meter is a battery operated (9V) device. When the battery is low, a “low- battery” indication appears on the display. The “Auto power off” feature automatically turns off the meter when no operation is detected for 15 minutes, thus helps to extend the battery life.   

Advance Features of Clamp Meter:

Several digital clamp meters offer a wide variety of advanced features which ultimately help an electrical engineer to a great extent. These features are:

1.  PC Interface – Clamp meters also come with PC interfacing serial ports to facilitate data transfer to computer for further analysis of data and report generation.
2. Data Logger – Some clamp meters have internal memory capable of holding the measured values to be used later on.
3. Inrush Current measurement – This feature allows the clamp meter to measure the high inrush current usually encountered during motor starting.
4. Autoranging – Automatically sets appropriate measurement range thus, avoids manual selection of range.

Safety Requirements and Standards:

The AC/DC clamp meters are designed accordingly to safety standard IEC61010-1 and IEC 61010-2-032 to meet the safety requirements for electrical measuring instruments and hand-held meters. They also comply the European standards 89/336/EEC for Electromagnetic Compatibility and 73/23/EEC for low voltage  


A few things should be followed so as to ensure that these meters last long in the harsh environment encountered in the field. The checks to be carried out are –
1.  Keep the meters in their safety cover or carry bag after the use to avoid ingress of moisture, dust etc, and shocks and damage.
2.  Do not store these meters in a strong magnetic field to avoid loss of accuracy. Electrical noise, unwanted signals or intense electromagnetic fields in the vicinity may disturb the measuring circuit.
3.  All meters are very fragile and hence should be handled with care.
4. Do not expose the meters to extreme hot or cold temperature and moist atmosphere.
5. Always select the proper range and nature of circuit i.e. AC or DC.
6. Always inspect the meter and test leads for any sign of damage or abnormality, such as broken or cracked, leads before use.

Friday, 3 February 2017

Ancillary services for Indian electric market

In a vertically integrated power system, one organization carried out all the work of electricity generation, transmission and distribution. Example is the erstwhile State Electricity Boards in India. Power industry throughout the world is undergoing the restructuring process and is adopting the deregulated structure for better utilization of resources and for providing quality services to its consumers at an economical price. 

The introduction of deregulation has brought in several new entities and some form of competitive electricity market. The vertical integrated utilities were separated into Generating companies (Gencos), Transmission Companies (Transco’s) and Distribution Companies (Discos). Apart from these three entities,  entities such as System Operators, Market Operators, Regulators etc were also formed. 

Central Electricity Regulatory Commission (CERC) Regulations 2010 defines Ancillary services as those services that are necessary to support the power system operation in maintaining power quality, reliability and security of the system or the grid. Examples are active power support for real time load following, reactive power support, black start, voltage control support etc.

In the deregulated environment, ancillary services are no longer treated as integral part of the electric supply. The system operators have to purchase these services from ancillary service providers. The CERC Regulation, 2010 made operation of ancillary services as an exclusive function of Regional Load Despatch Centre (RLDC). In the Central Advisory Committee meeting of CERC, held on 14th March 2012, there was a general consensus on the need for introducing ancillary services to enhance the secure and reliable operation of Indian power system.     

Main ancillary services under consideration in India:

Currently three main types of ancillary services are under consideration in India and they are:
1.      Real power support service or Frequency support ancillary service or Load following,
2.      Voltage or Reactive power support services, and
3.      Black Start support service.

Real power support service or Frequency support ancillary service or Load following:

In India, the real power support or the frequency support services are to be provided by generating station or any other authorized entity on behalf of the generating station. The services/capacity of the said station should be available for despatch as required by the nodal agency i.e. RLDC to support the system frequency. 

Considering the Indian power system as a whole there are cases when certain surplus energy, particularly from Captive power plants, lie un-utilized at some point of time at some location. At the same time some portion of the system is facing power shortage and carrying out load shedding to cope up with the situation. 

Therefore, there is an urgent need for service mechanism such as Frequency Support to properly utilize these unused capacities to enhance the Grid security. Initially generators having surplus generation, either because of un-requisitioned quantum by the beneficiaries or quantum of generation which could not find buyers or captive generation capacity, may bid for the frequency support when their services are sought upon by the system operator. 

Frequency support services can also help to mitigate the intermittent nature of renewable energy sources such as wind and solar farms. At this juncture it is worth mentioning that Indian government has set some very ambitious targets towards renewable energy generation particularly from wind and solar.     

Eligibility Criterion and Implementation
All the producers and the regional entities which are members of the scheduling and deviation settlement mechanism for real and reactive power are entitled to participate in the ancillary market, but the condition is that they must have relevant telemetry facilities. 

No other No Objection Certificate (NOC) or clearance, other than that issued by the respective RLDC/SLDC for participation in the Day-ahead Market (DAM), is required. The Frequency Support Ancillary Services (FSAS) are to be implemented through bidding in the power exchange. The participants are free to bid in any of the Power Exchanges of the country for ancillary services. The bids for FSAS to be dispatched on next day are to be opened up after the closure and clearance of the day-ahead market. Time-block-wise bids with the quantum, price and the location (where services are to be given) are to be submitted for the next day despatch.  

Reactive Power Ancillary Services

Unlike the frequency, voltage is a local phenomenon, and hence the requirement for reactive power support from capacitors or reactors at the different sub-stations or generating stations may vary. Thus, reactive power ancillary services are also in the list of ancillary services in India. Although there is a provision in the IEGC regulations and according to which proper voltage profile is to be maintained at all interchange points between the control areas in the Indian power grid.

However this is not sufficient and there is an urgent need for reactive power support to be added in the ancillary services list. Whenever there is persistent low voltage profile at one or more points in the system (this may be frequent during agricultural season), the system operator should have the voltage support ancillary tool in his armory. 

The voltage support ancillary service provider may also bid through the power exchange. Since the reactive power and hence the voltage support is a local phenomenon and their requirement are different at different locations, therefore mobile reactive power supports on trailers etc. can be very useful in the Indian power system. It is supposed that initially the government transmission companies will provide the mobile reactive power support and further opening up of the scenario will depend on their outcome.      

Black Start Ancillary Services

Black start is the process of restoring a power station to operation without relying on the external electric power from the transmission network. Normally the electric power required by a plant for its operation is provided by its own generators. If all the generators of a generating plant are out of service then to restore the generation, the station requires the electric supply externally, drawn from the transmission line connected to the station. In the event of power outage in a wide area, the transmission lines are also out of supply. In the absence of transmission line or grid, the so called Black Start facility is required.   

The Central Electricity Authority (CEA) Regulations 2007 mandates the Hydel power stations in the country to provide the Black Start facility. There is a provision of incentives to such service providers who offer their services (black start services) when asked by the system operator. Black Start Ancillary Services (BSAS) are to be paid when it is required by the SLDC i.e. the nodal agency. The generators capable of providing the start up power are to be paid for one day capacity charges for their services. The quantum of energy supplied during the restoration process is paid (energy prices are paid the BSAS provider) at twice the energy charges as determined by the Commission.  

Ref.: “Introduction of Ancillary services in Indian Electricity Market”, Central Electricity Regulatory Commission, New Delhi, April 2013

Monday, 30 January 2017

Role of Simulation Softwares in Solar PV plant Design and Operation

The performance of a Solar PV plant depends on the solar irradiation, the optimum tilt angle, ambient temperature, design parameters, quality of modules, efficiency of inverters etc. Earlier the expected generation output, losses in cables & equipments, voltage drop, lower and upper range of array voltage etc. were manually calculated. Now-a-days this tendency is fast being replaced by advanced simulation software, particularly in the case of solar PV plants with significant capacity.

Function of Simulation Softwares in plant Design and Operation:

Softwares are used as essential tools in the design, construction, operation and maintenance of Solar PV plants. They help to produce solar PV generation assessments, and site-specific production forecast accounting the location latitude and longitude, weather condition, shadow effect etc. These softwares lend a hand to optimize design configurations and system layouts, test the system performance. Economic evaluation and payback period calculation are also facilitated by these softwares. They also make possible the integration of PV plant output to the Utility grid, monitoring and control of the plant health, thus enhancing the operation of the PV plant.

Popular softwares:

There are several softwares available for assisting the solar PV system designing. The popular are:

1.       PVSYST
2.       PVSOL
3.       Solar Advisor Model (SAM)
4.       SMA off-grid Configurator
5.       Solar Pro
6.       PV Design Pro
7.       HELIOS 3D

PVSYST is one of the oldest and trusted PV designing software developed by the University of Geneva. The software offers a wide range of features, a few are –

1.Complete designing of off-grid and grid connected solar PV system.
2.Complete data base of solar modules and inverters.
3.Meteorological data of a large number of stations and sites across the world. Data of new sites can also be imported.
4.Access to PVGIS and NASA database for import of irradiation data.
5.Enables economic evaluation and payback period.
6.Predicts and asses the module behaviour under varying irradiation, ambient temperature and shading scenarios.

PVSYST software has two modes:
1.       Preliminary mode, and
2.       Project design mode.

In the preliminary mode one can get the approximate value of power generation. Project design mode allows user defined values for inverter efficiency, losses and shading effect. The results of these softwares are in the form of report, tables and graphs. The software is available in a trial version with one month access period. Cost of the software depends on its version and the number of design to be carried out per month.     

 Free Softwares:

Some free to download softwares such as PVGIS Estimation Utility, SMA Sunny Design etc are also available which can be used in the design of solar PV system.

PVGIS Estimation Utility is one such software which is freely available. With the help of this software one can calculate the output of a proposed solar PV plant, optimize the design and can have a fair idea about how the PV system is going to perform when completed.

Another free software is “SMA Sunny Design” by renowned solar inverter manufacturer SMA. The software generates detailed reports in “pdf” format of the proposed solar PV plant. The typical input required are the number and type of PV module to be used, location details, roof pitch etc. The software is able to compare the performance of PV panels of different types, makes and models. Although the software has the database of most of the solar PV panels, but one can have the option of feeding his/her own PV module details.

How the Software help out in plant Operation:

After the successful commissioning of a Solar PV plant, the next important activities are monitoring and operation & maintenance of the plant. There are softwares that help in carrying out these works also. The software can indentify under-performing plant and arrays, and thus help in increasing the power production. Incoming data from the PV modules, instruments to monitor the ambient, inverters, transformers and grid interfacing equipments are analyzed. Smart and advanced sensors and data loggers collect this information that affect the PV plant’s performance, and allow the software to create real time performance models. Variances are detected, and notifications and alarm messages are given to the concerned agency/ person.

Thus these softwares can create custom analytics, alerts, contracts and reports. They also helps in streamlining the operation & maintenance activities, and hence reduces Mean Time to Repair (MTTR). They also help in forecasting the power generation of the PV plant based on the weather forecast.  

 One such software is the Qantum Solar Monitoring and O&M software.

Friday, 27 January 2017

Digital Multi-Meters: A very handy tool for Electrical Engineers

An electrical engineer and electrician must be familiar with a variety of test and measurement instruments. They need to know how to use these instruments in a safe and proper way under different working conditions. It is important to use the right tools and instruments when working with electricity. Appropriate equipments can make a hard task easy and at the same time wrong selection can make an easy job difficult and dangerous.

This article looks at the most common type of meter available with an electrical engineer or electrician; i.e. the Multi-meter. 

Another versatile and handy instrument for an electrical engineer, particularly in the Solar PV field, is the digital clamp meter

Multi-meters are hand-held instruments designed to measure more than one electrical value; for example DC and AC voltages, DC and AC current, resistance etc. They are also used to check the continuity of conductors or to check the diode. Figure 1 shows the icon of some of the electrical quantities measured by a multi-meter.

Fig.1: Icon of some of the electrical quantities measured by a multi-meter.

In other words, a multi-meter is a measuring instrument that combines an ammeter, a voltmeter and an ohmmeter to measure the current, voltage and resistance in a circuit; means no need to carry different meters for measuring different values.

Digital Multi-meter:

Both analog and digital multi-meters are available, but the digital version has superseded the analog one. Digital Multi-meters (DMM) has a digital display to show the measured values, a dial or selector switch to change the mode of the meter, and connecting terminals. Figure 2 shows a low cost commonly available DMM.

Fig. 2: Low cost commonly available DMM.

Accessories such as a pair of red and black probes, is also provided with the meters. The black probe is always considered as the negative probe and is connected to the common terminal. Figure 3 shows the probe provided with the DMM.

Fig. 3: Probe provided with the DMM.

System with Harmonics:

When harmonics is present in the system, only true RMS meters can provide accurate measurement   of AC values. Harmonics are frequencies that are multiples of the fundamental frequency (50 Hz in India) and can cause distortion of basic AC waveform. The common loads which causes harmonics in the system are computers, fluorescent luminaires with electronic ballast, inverters etc. These electrical loads are also called Non-linear loads as their impedance are not constant.

Working of Digital Multi-Meter:

The basic circuit of a Digital Multi-Meter is always a DC voltmeter. The AC quantity is rectified into DC with the help of rectifiers and filters. All the quantities are digitised using an Analog to Digital Converter (ADC) and displayed in the digital form on the display.

Figure 4 shows the internal circuit of a commonly available Digital Multi-Meter.
Fig.4: Internal circuit of a commonly available Digital Multi-Meter.

Advantages of Digital Multi-Meter:

Digital Multi-Meters have the following advantages over analog:
1.       Cheap and compact,
2.       Accuracy is very high,
3.       No loading effect,
4.       Reading of values is much easier,
5.       Can be interfaced with external equipment,


“Always read and follow the manufacturer’s instructions that are supplied with the Multi-meter. Equipments may be damaged badly and or the user may be seriously injured if proper safety procedures and instructions are not followed.”
Safety is very important when using test and measurement instruments. Many a times, the meter is used to make the measurement while the electrical circuit is energized. Ensure to follow the regular and standard safety procedures when working on live circuits. A safe working practice is always mandatory. The following safety tips are recommended-

1.       Ensure the correct position of selector switch,
2.       Do not be alone when working on live circuits,
3.       Keep your hands dry when taking measurements,

4.  Use rubber gloves and wear shoes when taking measurements on energized circuits.

Monday, 26 December 2016

About the Solar Charge Controller

A solar PV system has several components. Apart from the solar PV panels, it has charge controller, inverter, battery bank, supporting structure, protective fuses, breakers & surge protectors, cables etc. All the components other than solar PV panel are collectively called Balance of System (BoS). A well designed system is required for the smooth and reliable operation of the Solar PV plant.

What is Solar Charge Controller and how it works?

A Solar Charge Controllers (S.C.C.) or simply Charge Controller monitors and controls the power output from the solar PV panels and the battery. The Controller controls the flow of charge into the battery while charging from the solar PV system, thus prevents overcharging of batteries. It detects the status of battery charge by measuring the terminal voltage of the battery.

In overcharge condition, the battery terminal voltage increases above a certain level. When the battery reaches overcharge status, as shown by the measured voltage, the charge controller cuts off the solar PV supply to the battery.

As the connected load continues to use the battery energy, the terminal voltage of the battery drops down. This drop in voltage is also detected by the charge controller as it is continuously monitoring the activities. Whenever the battery voltage reaches the normal operating range, the battery is connected back to the solar PV system, by the charge controller, for regular charging.    

Similarly, the charge controller also controls the discharge from the battery. It prevents deep discharge of the battery. In deep discharge condition, the battery terminal voltage decreases below a certain level. This happens because of excessive drainage of charge from the battery, probably due to prolonged use of significant load. As the battery gets into deep discharge state, the charge controller detects it from the measured voltage and disconnects the battery from the circuit, so that no current can be further drawn from the battery. The life of a Lead-Acid battery very much depends on the Depth of Discharge (DoD).

"For example, as per Luminous, a renowned solar battery manufacturer in India, solar Flooded Lead-acid Tubular batteries have a life of 1500 cycles at 80% DoD, 3000 cycles at 50% DoD and 5000 cycles at 20% DoD."
Thus, both overcharging and deep discharging of battery or battery bank must be avoided to enhance the battery life.

Features available in Charge Controllers:

A Charge Controller usually/ may have the following features:

1.       LED or LCD display of various parameters or functions,
2. Automatic Temperature Compensation feature; automatically adjusts the battery charging according to the ambient temperature,
3.  User defined setting of battery voltage and type,
4.  Protection for low voltage, overvoltage and reverse connection,
5.  Automatic priority selection feature,
6.  Equalization feature.
Omission or addition of certain feature may happen, and it depends on the manufacturer.

Types of Charge Controllers:

The two commonly available types of Charge Controllers are:

     Pulse Width Modulation (PWM) Charge Controller, and
2.  Maximum Power Point Tracking (MPPT) Charge Controller.

Pulse Width Modulation (PWM) Charge Controller:

PWM Charge Controller is a solid state controller that usually works on three step charging algorithm. It has a semi-conductor switch which is switched ON and off by PWM at a variable frequency to maintain the battery voltage. When the battery voltage reaches the pre-specified value, the charging current is reduced as per the charging algorithm to avoid heating and gassing of the battery.

The PWM charge controller adjusts the charging according to the battery condition and requirement by controlling the speed of the switching element, which breaks the PV output current into pulses at some constant frequency and varies the width and time of pulses to regulate the amount of charge flowing into the battery.

Pulses of current helps the battery as it mixes the electrolyte, clears the lead electrode and prevents sulphation.

PWM charge controller maintains the battery capacities to 90-95% and has the ability to recover lost battery capacity. This helps in equalizing drifting of battery cells, automatically adjusts battery aging, increase the charge acceptance of the battery and self regulates the voltage drops and temperature effects of the solar PV system. These charge controllers are cheap and available in a wider range of capacities.

PWM charge controller is a good low cost option for small roof top solar PV systems where the ambient temperature is moderate or high.

Drawbacks of PWM charge controller:
1. The controller voltage must match the battery bank voltage, and
2. Usually the maximum current capacity of PWM charge controller is limited to 60 A.

Maximum Power Point Tracking (MPPT) controller:

Maximum Power Point Tracking (MPPT) controller is a charge controller with an additional device called the Maximum Power Point Tracker. These controllers provide a digital tracking of the PV panel output and compare it with the battery voltage. It then works out the maximum power that the panel can flush out to charge the battery or to the load. It tracks the optimum voltage so as to get the maximum amperage to charge the battery. Actually it is the amperage which makes sense for the battery.

MPPT charge controllers have higher efficiency, thus higher output power and overall better battery management than PWM charge controllers. These charge controllers continuously adjust the load on the solar PV system under varying operating conditions and keeps it operating at the maximum power point. As mentioned earlier, the controller checks the output of the PV array and compares to the battery voltage. It then calculates the maximum power that the PV array can produce. Accordingly, the controller converts the PV output voltage and converts it to the optimum value that fetches the maximum current into the battery or the load.

MPPT power varies according to the weather conditions, i.e. solar radiation, ambient temperature, and cell temperature. The voltage point at which the PV system produces maximum power is called Maximum Power Point (M.P.P.). Thus, the MPPT charge controller acts as a DC voltage converter which converts the PV array voltage into a voltage that fetches maximum power. The converter converts the DC input from the PV into a AC voltage and converts it back to DC matching the battery voltage. A Buck converter is used to step down the voltage, whereas a Boost converter is used to step up the voltage. They are used in PV systems of higher capacity, although MPPT charge controllers with smaller capacity say 17 A, is also available in the market.

For a PWM charge controller, the output current is the same as the input current, whereas for a MPPT charge controller, the output power is the difference of the input power and controller losses. With an MPPT charge controller employed, the system can deliver 20 to 45% more power in winter and 10 to 15% more in summer. The actual gain may vary depending on the weather temperature, state of the battery charge etc.

Figure 1 shows a 12 V, 17 A MPPT solar charge controller of Su-Kam make which is available in approximately 2,300 INR (in Bhopal, MP).

Fig.1: 12 V, 17 A MPPT solar charge controller of Su-Kam make 
MPPT charge controller has the following advantages:

1.  More effective in low temperature and cloudy days,
2. Have better efficiency in the range 93-97%. ( much better than PWM controller).
The drawbacks are complex circuit and comparatively higher cost.

In some solar PV systems, the charge controller and the inverter are collectively housed in a single unit and are called the Power Conditioning Unit (P.C.U.). Batteries are also among the key elements used in off-grid solar PV systems and hence one should know a bit about these storage devices.

Also read:

Tuesday, 13 December 2016

Net Metering arrangements for Roof top Solar PV Systems

Most of the Indian cities, towns and villages have nearly 250 to 300 days of sunny days and thus roof top solar PV system can be a very attractive option. The Jawaharlal Nehru National Solar Mission (JNNSM) with the goal to encourage roof top solar PV systems in India has implemented a separate scheme known as “Roof top PV and Small Scale Solar Generation Program”. 

In my opinion, Roof top solar PV systems are going to witness appreciable capacity expansion particularly on the residential and commercial buildings in India and can be seen as a significant business opportunity.

Types and Models of Roof top PV systems:

The roof top solar PV system can be a grid interactive system or a stand-alone system. In grid interactive system, the DC power produced is converted to AC power, and after due conditioning this power is fed to the captive loads of the premise. The excess power is injected to the utility grid through 11 kV or LT lines, depending on the size of the solar PV system. When sufficient solar PV power is not available, the loads are fed from the grid supply. 

Although the grid interactive solar PV system is not supposed to have a battery pack, but to enhance the reliability a minimum battery backup of 1 hour is technically recommended. There is some minimum capacity constraints ( 1 kWp) below which the system can not be grid interactive.    

Different arrangements of Roof top solar PV system:

Two different arrangements of Roof top solar PV system do exist. They are:
1.      Self owned roof top solar PV system, and
2.      Third party owned roof top solar PV system.

In the self owned arrangement, the roof top owner or the premise owner installs the solar PV system, either of its own or with the aid of a system supplier. The power produced is first used to feed the captive loads within the premise and the excess power is fed to the grid.

The third party roof top solar PV system can be an attractive and viable model particularly for residential sector in India and seems to be a good business and job provider. In this model a developer or intermediate agency called the “third party” design, install and lease out the solar PV system to interested roof top owners who in turn pay them a monthly rent. 

This model offers some great advantages; 
(i) the roof top owner does not have to invest for the PV system, and
(ii) does not have to bear the brunt of the technological risks involved in a fast changing solar PV business.

Net Metering arrangement:

In both the models, the feeding of excess energy to the grid or the drawal from the grid in case of insufficient solar power generation is through a net metering arrangement. 

Two meters have to be installed at the premise and will replace the existing meter. One, the solar energy meter to record the energy produced by the PV system and other the net meter, a bi-directional meter, to record the import/export of energy by the consumer from/to grid. The point of solar power injection may be in between the load and the bi-directional meter. These meters are supposed to have the MRI and AMR facility and should adhere to the standards specified by the CEA regulations.

The net energy (kWh) injected to the grid during a billing month/period is supposed to be carried forward. At the end of the financial year any net energy credits which is yet not adjusted is paid to the owner of the premise/consumer by the distribution company. To promote the scheme, certain states have waived off the wheeling charge, cross subsidy surcharge and other similar charges/levy for a period of 5 years.  

If the cost of solar energy and the grid energy is kept the same, there may not be any significant financial benefit to the residential consumers, although the commercial consumer paying at a much higher grid tariff may get benefited. To get more, the residential premise owners have to install a much larger PV system. 

Policy on roof top solar PV systems of certain states in India has put a cap on the solar generation which is about 90 % of the annual energy drawal. Apart from the net metering arrangement the roof top owner  can also avail the available subsidy (currently 30 %) from the Ministry of new and Renewable Energy (MNRE).

Friday, 9 December 2016

Safety in Power Plants, Stations and Electrical Networks: A Collective responsibility?

Indian electrical power system consists of many generating stations, sub-stations, and transmission & distribution lines of voltage range 1200/ 765/ 400/ 220/ 132/ 66/ 33/ 11 kV. All the associated equipments of power system are monitored, attended, operated and maintained round the clock for un-interrupted and reliable flow of electricity throughout the country. New construction or capacity addition activities are also carried out simultaneously. Most of the operation and maintenance activities are done by regular engineers and technicians of the concerned organization, whereas bulk of the construction works is carried out through outsourcing.

The electrical and electronic equipments and systems used in any power system network are designed in such a way that they are safe during normal operation, but in case of mal-operation or faults they can be very dangerous.
This article is supposed to throw some light on safety aspects, and to grab the attention of our young engineers and technicians.

What is safety?

What the word safety means as far as electrical power stations and networks are concerned?

“Safety may be interpreted as proper planning of task, proper usage of safety tools and equipments, following safety procedures, exercising good judgement and intelligent supervision.”

Fig 1: A combination of unsafe working conditions,and unsafe activities.

 Analysis show that majority of accidents were preventable.

Safety: A Collective responsibility

With a massive growth and expansion of generating stations, substations, lines and associated systems, safety at work place is of prime importance. Accident do not “just happen”, but they are the outcome of unsafe working conditions, unsafe activities or a combination of both. 

Then who is responsible for the “safe working environment” in electrical plants and networks?

It is our, i.e. of electrical engineers, technicians, and contractors, collective responsibility to implement safety standards and maintain a safe working environment in the best possible way.
We must learn from past mistakes, evolve gradually and move towards an accident free atmosphere. The presently followed safety standards should be enhanced to minimize, if not possible to eliminate, accidents and injuries.

Rules, Act and Code to be followed:

One should follow the safety policy, statutory provisions pertaining to safety, responsibility assignment, hazard identification, and personnel protective equipments and tools.

All the electrical engineers/ technicians working on electrical power projects in India, must ensure compliance with the requirements of Indian Electricity (I.E.) Rule 1956, Indian Electricity Act 2003, Indian Electricity Grid Code and Central Electricity Authority (C.E.A.) Regulation 2010.

Role of Electrical Engineers:

As an electrical engineer it must be our policy to perform each task in the safest possible manner, together with good practice. The health, safety and well-being of our workers and all those who are likely to be affected, are our responsibility. Safety aspect should be kept at par with our business objectives. Not only the engineers, it is the duty of each worker engaged in power system construction, operation and maintenance activities to exercise due care and caution for his/ her own safety, of fellow workers, and the concerned equipment and system.

As an engineer, we must:
Ø  Provide safety information, instruction and training to the team,
Ø  Ensure that tasks are allocated to competent workers,
Ø  Ensure safe and proper handling and use of equipments,
Ø  Provide and maintain a safe plant and Equipment, and
Ø Consult with our fellow engineers, sub-ordinates, and technicians on matters affecting the safety.


Prevention of accidents or mis-happenings requires a whole hearted co-operation of all the concerned. Usually it’s the capable and mentally alert worker who avoids the accident. Good luck.