Associated Hazards and Safety Practices REVENUE METERING Associated Hazards and Safety Practices

Transformer-rated Meters Application and Components Current Transformers Voltage (Potential) Transformers Transformer-rated meters are used because: Meters used directly on high voltages (over 480V) or currents (over 200A) could fail or explode.

Transformer-Rated Meters (cont.) Components Instrument transformers Test switches Transformer-rated revenue meter Transformer-rated meter base

Current Transformers For customers who use over 200 amps. Types Bar Window Switchgear Primary

Current Transformers (cont.) Ratio (Multiplier) _% of energy sent to meter. A common ratio is 200:5. This means that there is a multiplier of 40. Burden: Expressed in ohms and tells you the load on the secondary. Rate Factors: Thermal: How much the primary load current can be increased over it’s nameplate value.

Current Transformers: Nameplates Shorting Bar X1 X2 Voltage Rating Ratio Rate Factor Ratio

Current Transformers (cont.) Construction Shunting bar Primary (H1 or H2); Secondary (X1 or X2) Larger wire/few turns; smaller wire, many turns Lower current on output for meters

Current Transformers (cont.) Dangers of CT’s If you open the connections in a CT meter: The voltage across the secondary will increase rapidly toward infinity, which may cause the CT to explode. WARNING! Never open the connections in a CT meter

Current Transformers Connection Customer

Current Transformers Connection What happens when you take the meter out of the circuit? ? Customer

Current Transformers Connection A voltage is still induced onto the secondary windings of the CT. This leaves an open circuit. What happens when you take the meter out of the circuit? Customer Customer is still energized!

Current Transformers (cont.) Opening a CT Pull the meter Cut the secondary wire to meter Any way that opens the current path between the secondary of the CT to its return.

Voltage Transformers (VT or PT) Step down the primary voltage to lower levels that are safer and easier to meter. PT = VT Transformers are connected to the service voltage. Connected in parallel

Voltage Transformers (VT or PT) Typically used on systems with more than 600V. Transformers are connected to service voltage. Ratio: Percent of voltage sent to meter Burden: Expressed in VA and relates to the load on the secondary side of the potential transformers.

Voltage Transformers (cont.) Types of VTs Primary Secondary Rating VTs W= 12.5 va X = 25 va Y = 75 Z = 200 Zz = 400 M = 35

You are dealing with voltage (not current) Dangers of PTs Never shunt a PT You are dealing with voltage (not current) and you are connected in parallel (not series).

Types of Meter Bases Bypass Meter Bases Safety Sockets -energized or not? Green lever vs. red lever Jaws open but can be bypass Bypasses not designed to carry full load Cut off levers for current diversion Test switch provisions -transformer rated

Installing and Removing Meters Be safe! If hazards are present, do not work alone. When installing or removing the first priority is: ENSURING YOUR SAFETY!

Installing and Removing Meters (cont.) Never pull a meter under load. Disconnect meter by shutting off breaker. Verify that the power is disconnected at: The weatherhead. The transformer. Re-installing meter under load will cause sparking.

Installing and Removing Meters (cont.) Pulling transformer-rated meter without shunting current transformers . . . . Current transformers may explode! Customer will still be in power.

Socket Checks Determine if socket is wired correctly. Verify no backfeed or fault condition exists. Use meter socket check handout. Inspect for any missing knockouts or openings to energized equipment.

Socket Checks (cont.) Inspect for broken/misaligned socket terminals. Inspect for broken/cracked porcelain blocks. Ensure the socket base is properly secured and meter can be sealed.

Meter Installation Notify customer Use proper safety gear Socket check Visual inspection

Meter Removal A meter is not a load break tool! Deenergize the meter before pulling it. Notify customer Use proper safety gear Verify no load Visual inspection

Meter Selection Issues Typical misapplication of 5 point meter Wild leg in the wrong spot Single phase 120/240 vs120/208 (2S vs. 12S) Older 14S 240 volt meters -Actual voltage 277/480 120 volt 1S meter in a 240 volt 2S service

Detecting Current Diversions

Detecting Current Diversions

The photo on the top shows a 5-terminal lever bypass socket used with a Form 12S, 480 volt meter on 480 volt, 3 wire delta application The photo on the bottom shows the existing meter “can” retrofitted with a TS-SCB-1 block assembly and VT Pack. The VT Pack is mounted on the outsie of the socket with the CK-St-1 mounting kit.

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