In this section, we discuss the installation, commissioning and field testing of meters.
Energy Meters – Installation and Commissioning
The meters are connected before the consumer’s isolating device (Main Switch), which may be a moulded case circuit breaker, miniature circuit breaker or an ironclad switch fuse unit. At the time of commissioning, each meter is tested at site by the owner. A reference standard meter of 0.2 class or better is used for testing.
Supply Side Wiring
The supply side wiring is the responsibility of the utility and the following must be ensured while carrying it out:
a) The supply wires provided are of suitable rating.
b) In case of more than one meter on one service line, it is preferable to use bus-bars. When a number of meters are connected to single distributing mains for registering electricity supplied to different consumer loads,separate service lines – phase(s) and neutral, are used for each meter.Each independently metered consumer load is directly connected to distributing mains through its meter connected in specified phase sequence so as to meet accuracy requirements of relevant standard.
c) The supply wire is properly terminated.
d) The connection is as per connection diagram mentioned on meter.
e) Utility should use its own earthing for its devices.
Utility provides phase and neutral supply to the consumers. The neutral is used for carrying return current only. The neutral of one consumer should not be connected to other consumers who have independent and separate supply connection. Utility provides separate neutral to each consumer up the metering point and same is used by the consumer. The consumer ensures that all the correct wiring practices are followed and neutral is not looped with another consumer or meters in the same premises. Consumer should not earth the neutral after the metering point. Wherever there is multiple metern installations, bus bar arrangement is used for neutral, so that looping is avoided.
Installation of Meters and Verification of Connections
Apart from testing and calibrating the meters they must be properly installed as per the connection diagram. The points that must be kept in view while meters are installed are given in Box .
Box : Installation of Meters
a) Position of meter should be such that reading is easily visible.
b) Mounting of meter should be on solid wall or DP structure or on panel board.
c) Vertical mounting of meters should be ensured. The utility engineer should use a plumb bob and mark a vertical line prior to installation.He could also use a spirit level and put on the top of the meter after hanging on the screw hole. Alternatively, he should put spirit level on the edge of the terminal block to ensure vertical mounting.
d) For HT metering equipment, CTs should be right on the incoming side before the point of isolation.
e) The meter box should be sealed.
f)The meter recording should be checked at site.
The following should also be ensured:
a) Appropriate crimping device should be used for crimping the lugs.Thimbles should be of appropriate configuration (pin type, fork type etc.) to match with the terminal block for low current connection. For high current terminations, crimping should be used with cable crimping tools and multiple point crimping should be done for the lugs used for higher current ratings.
b) If the terminal block is of MS cage clamp type, there is no need to use any lugs and the copper cables can be directly terminated at the clamp.
c) The recommended tightening torque must be exerted on the screw to ensure proper tightening of the terminations. It is recommended to use proper tools, equipments for this purpose.
d) Usage of lugs as per the recommendation of manufacturer and ensuring proper crimping will protect the joints from failures.
e) For high current terminations, tensile test and shock test should be performed after crimping the lugs.
f)Where aluminium cable termination is to be done on copper bus bars or brass studs, bimetallic type of lugs should be used.
g) Some meters have lower terminal pitch. Because of this, cables foul with each other while installation. Proper cable size according to the meter rating should be defined.
h) Aluminium conductor cables should be replaced by copper cables for the whole current meters.
i)For indoor meters, the wiring should be done such that the cables enter the meter box from the bottom or rear side. This not only is aesthetic, but also prevents the service cable from tampers, etc.
The points that should be verified after installation of the metering system are given in Box.
Box : Points of Verification
i) Phase association
ii) CT polarity
iii) VT polarity
iv) Phase angles
v) Phase sequence
vi) System conditions – unbalanced capacitors
vii) Actual CT / VT ratio
Sealing Points
The meter seal should be tamper proof. The consumer should be briefed about seals. The sealing of all metering systems should be done at various points (as applicable) to avoid tampering. There should be at least one seal at all points mentioned below (wherever applicable):
a) CT Secondary Boxes (in addition to locking arrangement)
b) PT Secondary Box (in addition to the locking arrangement)
c) Meter Cabinet
d) Meter Test Block
e) Meter Terminal Cover
f)Meter Cover
g) Panel doors where CT and PT secondary circuits are terminated or where possibility for shorting or breaking exists and fuses/links are provided.
h) PT selector relay box where automatic change-over of potential supply to meter from one PT to another is provided
i) CT Primary Links and Top Covers
j) MD Reset Push Button
k) Boxes/Cabinets containing terminals for remote transmission of metered data via communication channels, junction boxes in the system and boxes wherein interface devices are mounted.
l)Meter reading port.Seals are necessary to guard against the tampering of connections and internal parts of a meter. Tampering of seals will give consumers access to th relevant part of a meter installation where s/he can manipulate the unit to record less energy leading to commercial loss. A seal is placed to detect unauthorized entry to the meter internals.
The effectiveness of the seal depends on the type of seal (whether it is tamper proof or not, whether a duplicate can be obtained or not, etc.), and the procedures used in tracking the seals.
The important points for seal management are given in Box .
Box : Seal Management
For an effective seal management system it is essential that:
i)The seals used are tamper proof, i.e., they cannot be removed and replaced by customers.
ii) The seals should be from such sources that duplicates should not be available or cannot be manufactured.
iii) The number of seals placed on each meter should not be very large, as this will cause logistic problems in managing and auditing the seals.
iv) A proper seal issuing and managing system should be put into place where location of each seal can be traced at any point of time. This covers tracking its total movement starting from ordering,manufacturing, procurement, storage, record keeping, installation, series of inspection, removal and disposal.
v) Seals must be stored securely and assigned to individuals responsible for their safekeeping.
vi) Seal audits should be checked routinely, particularly at the time of meter reading and also through audit checks.
Energy Meters – Installation and Commissioning
The meters are connected before the consumer’s isolating device (Main Switch), which may be a moulded case circuit breaker, miniature circuit breaker or an ironclad switch fuse unit. At the time of commissioning, each meter is tested at site by the owner. A reference standard meter of 0.2 class or better is used for testing.
Supply Side Wiring
The supply side wiring is the responsibility of the utility and the following must be ensured while carrying it out:
a) The supply wires provided are of suitable rating.
b) In case of more than one meter on one service line, it is preferable to use bus-bars. When a number of meters are connected to single distributing mains for registering electricity supplied to different consumer loads,separate service lines – phase(s) and neutral, are used for each meter.Each independently metered consumer load is directly connected to distributing mains through its meter connected in specified phase sequence so as to meet accuracy requirements of relevant standard.
c) The supply wire is properly terminated.
d) The connection is as per connection diagram mentioned on meter.
e) Utility should use its own earthing for its devices.
Utility provides phase and neutral supply to the consumers. The neutral is used for carrying return current only. The neutral of one consumer should not be connected to other consumers who have independent and separate supply connection. Utility provides separate neutral to each consumer up the metering point and same is used by the consumer. The consumer ensures that all the correct wiring practices are followed and neutral is not looped with another consumer or meters in the same premises. Consumer should not earth the neutral after the metering point. Wherever there is multiple metern installations, bus bar arrangement is used for neutral, so that looping is avoided.
Installation of Meters and Verification of Connections
Apart from testing and calibrating the meters they must be properly installed as per the connection diagram. The points that must be kept in view while meters are installed are given in Box .
Box : Installation of Meters
a) Position of meter should be such that reading is easily visible.
b) Mounting of meter should be on solid wall or DP structure or on panel board.
c) Vertical mounting of meters should be ensured. The utility engineer should use a plumb bob and mark a vertical line prior to installation.He could also use a spirit level and put on the top of the meter after hanging on the screw hole. Alternatively, he should put spirit level on the edge of the terminal block to ensure vertical mounting.
d) For HT metering equipment, CTs should be right on the incoming side before the point of isolation.
e) The meter box should be sealed.
f)The meter recording should be checked at site.
The following should also be ensured:
a) Appropriate crimping device should be used for crimping the lugs.Thimbles should be of appropriate configuration (pin type, fork type etc.) to match with the terminal block for low current connection. For high current terminations, crimping should be used with cable crimping tools and multiple point crimping should be done for the lugs used for higher current ratings.
b) If the terminal block is of MS cage clamp type, there is no need to use any lugs and the copper cables can be directly terminated at the clamp.
c) The recommended tightening torque must be exerted on the screw to ensure proper tightening of the terminations. It is recommended to use proper tools, equipments for this purpose.
d) Usage of lugs as per the recommendation of manufacturer and ensuring proper crimping will protect the joints from failures.
e) For high current terminations, tensile test and shock test should be performed after crimping the lugs.
f)Where aluminium cable termination is to be done on copper bus bars or brass studs, bimetallic type of lugs should be used.
g) Some meters have lower terminal pitch. Because of this, cables foul with each other while installation. Proper cable size according to the meter rating should be defined.
h) Aluminium conductor cables should be replaced by copper cables for the whole current meters.
i)For indoor meters, the wiring should be done such that the cables enter the meter box from the bottom or rear side. This not only is aesthetic, but also prevents the service cable from tampers, etc.
The points that should be verified after installation of the metering system are given in Box.
Box : Points of Verification
i) Phase association
ii) CT polarity
iii) VT polarity
iv) Phase angles
v) Phase sequence
vi) System conditions – unbalanced capacitors
vii) Actual CT / VT ratio
Sealing Points
The meter seal should be tamper proof. The consumer should be briefed about seals. The sealing of all metering systems should be done at various points (as applicable) to avoid tampering. There should be at least one seal at all points mentioned below (wherever applicable):
a) CT Secondary Boxes (in addition to locking arrangement)
b) PT Secondary Box (in addition to the locking arrangement)
c) Meter Cabinet
d) Meter Test Block
e) Meter Terminal Cover
f)Meter Cover
g) Panel doors where CT and PT secondary circuits are terminated or where possibility for shorting or breaking exists and fuses/links are provided.
h) PT selector relay box where automatic change-over of potential supply to meter from one PT to another is provided
i) CT Primary Links and Top Covers
j) MD Reset Push Button
k) Boxes/Cabinets containing terminals for remote transmission of metered data via communication channels, junction boxes in the system and boxes wherein interface devices are mounted.
l)Meter reading port.Seals are necessary to guard against the tampering of connections and internal parts of a meter. Tampering of seals will give consumers access to th relevant part of a meter installation where s/he can manipulate the unit to record less energy leading to commercial loss. A seal is placed to detect unauthorized entry to the meter internals.
The effectiveness of the seal depends on the type of seal (whether it is tamper proof or not, whether a duplicate can be obtained or not, etc.), and the procedures used in tracking the seals.
The important points for seal management are given in Box .
Box : Seal Management
For an effective seal management system it is essential that:
i)The seals used are tamper proof, i.e., they cannot be removed and replaced by customers.
ii) The seals should be from such sources that duplicates should not be available or cannot be manufactured.
iii) The number of seals placed on each meter should not be very large, as this will cause logistic problems in managing and auditing the seals.
iv) A proper seal issuing and managing system should be put into place where location of each seal can be traced at any point of time. This covers tracking its total movement starting from ordering,manufacturing, procurement, storage, record keeping, installation, series of inspection, removal and disposal.
v) Seals must be stored securely and assigned to individuals responsible for their safekeeping.
vi) Seal audits should be checked routinely, particularly at the time of meter reading and also through audit checks.
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