Troubleshooting: Why a Wattmeter or Var Meter is Not Showing Value When Connections are Correct

Working on items in a substation is not a task for the uneducated. Relying on platforms like Quora for substation-related issues is not advisable. Electrification is a discipline that requires extensive knowledge, and any company operating a substation should have qualified, experienced, and professional high-voltage power engineers on staff. If not, it’s crucial to hire one to avoid putting yourself or others at risk.

Check Instrument Ratios

You might want to verify that the potential transformer (PT) and current transformer (CT) ratios are correct for the new instruments. A mismatch in these ratios would explain incorrect readings. Always ensure that these components are properly adjusted to match the power meter or var meter’s specifications.

Assessing New Instruments

While an instrument may appear new, it is erroneous to assume that it is functioning correctly. The most probable reason for a wattmeter or var meter not showing a value (other than a zero reading) is an incorrect connection. Some instruments are self-powered from the measured voltage, whereas others, especially digital meters, require an auxiliary supply. This supply is often DC from the substation’s battery system; otherwise, a digital meter would not display a zero or very low reading.

Wiring and Connection Issues

It's crucial to check the wiring of the new instruments. If the wiring is incorrect, the voltage inputs and current inputs may be incorrectly connected. I have encountered this issue with a single-phase meter, where the voltage was measured from the red phase, but the current was connected to the blue phase instead of the red phase. This mistake can result in negative power readings, causing the meter needle to monitor in the opposite direction.

Correct Wiring Phases

To prevent such issues, ensure that the correct phases are connected:

For voltages, connect ABC or RYB (Red, Yellow, Blue) to the appropriate phases on the meter. For currents, wire the ABC or RWB (Red, White, Black) correctly. Incorrect wiring can lead to negative readings and improper meter function.

Additionally, an analog meter will show negative power and drive the pointer in the opposite direction, making it appear as if the meter is not moving. If you suspect any wiring issues, it’s best to consult a qualified testing and commissioning engineer. If you are the operator, your current level of training may not be sufficient to troubleshoot such issues. Pass the problem to someone with the appropriate skills and knowledge.

Always prioritize safety and ensure that you have the necessary expertise to handle substation equipment. If you are unsure or inexperienced, it’s advisable to seek professional assistance to avoid potential hazards.