We reasoned out the purpose of the ABT mechanism in our previous post. Here we shall dive deep to further metering mechanism. Before we go for it, it’s imperative for the reader to understand the world of Energy Meters. I have compiled all the posts under the chain of “Energy Meters” here. And to have further perspective, one can refer them as below:
Having clear perspectives about the energy meters, it’s simpler to understand how ABT meters do function. But before we go for the function, let’s understand the application of them. Basically, utilities find a variety of purposes for deployment of ABT meters. ABT meters are not just for the entities who distribute the electricity, rather they stand equal importance for the utilities engaged in electricity generation. In India, as per IS 15959:2001, we can categorize the ABT meters into three broad categories, viz Category A, Category B, and Category C meters. The entire post is confined to the IS 15959:2011, that’s Indian standards in compliance to IEC 61334-6. Since the IS 15959:2011 applies to all the utility-scale meters, ABT meters also follow the same.
Category A: These meters are basically used for Energy Accounting and Audit purpose.
Category B: These are basically boundary meters, and are deployed at the substations where generation merges with transmission and transmission merges with the distribution.
Category C: These meters are basically installed at the consumer end, and hence are capable to read the highest No of parameters.
Generally, these are 3-Phase, 4-wire meters, and are of Four Quadrant, Bi-Directional power flow, a solidly earthed system with balanced and unbalanced loads for a power factor range from zero to unity (lagging and leading), with accuracy class 0.2s. The meter is a self-contained device for measurement of active, apparent and reactive energy and certain other parameters as per the Category and utility requirement. The ABT meters are being directly connected to 110 VAC (via PT or CVT having secondary voltage as 110 V), and CTs with a rated secondary current of 1 Amp.
Broadly the parameters being read by the meters can be classified into below categories:
- Instantaneous parameters (IP Data)
- Block Profile / Load Survey (LS Data)
- Daily Profile Parameters
- Parameters for Accounting and Billing
- General purpose quantities:
- Nameplate details
- Programmable parameters
- Events conditions
Each of the parameters can be identified using a unique OBIS (Object Identification System) Code, Interface Class, and other such attributes. Here we shall not indulge into the world of OBIS or COSEM (Companion Specification for the Energy Meters) or DLMS (Device Language Message Specification).
Below is a brief about a typical ABT meter, one may consider while understanding in deep:
The case makes the meter immune to vibrations and shocks in normal service and transportation; The construction of the meter shall be such as to permit sealing of the meter cover, terminal cover etc. independently to ensure that the internal parts are not accessible for tampering etc. without breaking the seals. The meter window is transparent.
Meters do filter harmonics prior it reads Wh, Vah, and VArh data, and will measure or calculate only the fundamental frequency. The 15 min interval measured Wh data would show +ve sign in case of net export from the substation bar and -ve sign in case of net import. And that’s how the register would move forward or backward when the energy is exported and imported respectively.
Immunity to external factors:
The meters are immune to external influences like magnetic induction, vibration, electrostatic discharge, switching transients, surge voltages, oblique suspension, and harmonics. The meter accuracy shall not be affected by AC / DC magnetic field up to 0.2 Tesla on all the sides of meter i.e. front, sides, top and bottom of the meter as per CBIP publication No. 304 with latest amendments. In case of such violation, it’d record it as a magnetic tamper.
- Meter body cover
- Meter terminal cover
- MD reset button
- Communication port
Resolution of the parameters being read:
- Voltage: 0.1 V
- Current: 0.001 A
- Power Factor: 0.001
- Energy: 0.001 MWh
- Demand: 0.1 KVA / KW
- Frequency: 0.001 Hz
Time of Day (ToD) / Time of Use (ToU):
Meter can store upto 8 time-zone data (e.g. 00:00 to 04:00, 04:00 to 08:00, 08:00 to 12:00, 12:00 to 16:00, 16:00 to 20:00 and 20:00 to 00:00). The meter contains a Real Time Clock (RTC) that runs on quartz crystal with an independent battery of power supply. This RTC helps meter in recording the data with real-time reference. These time-zones can be configured by the utility.
ABT meters do come with RS 232 port for serial communication. As per latest directives, all the ABT meters are DLMS compliant and hence, OEM specified software is not required to access the data. Using this port user can read the data and can also communicate the same to the remote servers via a GPRS modem. This post would help in understanding how a typical energy meter communicates. ABT meters do also come with an additional communication port, using which a local user can get the stored data using a portable Hand Hold Unit (HHU). Generally, ABT meters do store data over 15 min intervals.
ABT meters do come with below kinds of self-diagnostic features:
- Time and Calendar
- Real Time Clock (RTC)
- RTC Battery
- Non-Volatile Memory
- All Display Segments
ABT meters are subject to broadly three kinds of tests, viz. Type Test, User Acceptance Tests (UATs) and Routine Tests.
Type tests are to be carried out in compliance with IS 14697. Below are some of the featured criteria for the Type Test:
- Clearance and Creepage distance of the terminal block and between the terminals
- Terminal cover
- Temperature range (Operation range: -10 Deg C to +60 Deg C and Storage range: -10 Deg C to +70 Deg C)
- Relative Humidity (Annual mean <75%)
- Power consumption in voltage circuit (8 VA) and in Current circuit (1.0 VA)
- Influence of the supply voltage (0.7 to 1.2 Vref)
- Voltage dips and Interruptions
- Short time over current
- Influence of heating
- Immunity of Electromagnetic interference (Electrostatic discharge, Electromagnetic HF and Fast Transient burst)
- Radio Interference Suppression
- Measurement Accuracy
For the User Acceptance Tests, generally below kinds of tests are being carried out on the user selected meters on supplier’s premise:
- 15 min block average frequency tests
- 15 min block net active power register
- Net kVArh High registration in all four quadrants when voltage is above 103% of VREF
- Net kVArh registration in all four quadrants when the voltage is at VREF.
- Net kVArh Low registration in all four quadrants when the voltage is 97% of VREF.
- Net kVArh Low registration in all four quadrants when the voltage is below 97% of VREF.
- Test for confirmation of midnight energy banking in power ON & power OFF conditions.
Routine Tests are basically being carried out by the OEM as a part of their Quality Assurance and Quality Control Processes (QA/QC). And such tests are being carried out on all the meters being supplied.
Utility officials do visit the OEM site for inspection and verification. It is also expected that the meter manufacturer does give proper training to the officials of the utility, along with all detailed documents such as drawings, design, catalogs, operating manuals, mounting instructions, etc.
Since the parameters being read by the ABT meters are very exhaustive and classified as per the meter categories, we shall share the same in a separate post.