Electrical Energy Metering: Transformers, Meters and Wiring
AI Summary: An electrical energy metering system consists of energy meters, current transformers, voltage transformers and secondary circuits. Procurement focuses on accuracy class, rated current, transformation ratio, wiring method and calibration. High currents must be measured through transformers; incorrect ratios and polarity will cause inaccurate metering.
Procurement Checklist
| Review Item | Selection Points |
|---|---|
| Meter Accuracy | Different accuracy classes for billing and assessment metering |
| Transformer Ratio | Match with load and meter |
| Polarity and Phase Sequence | Correct wiring to prevent reversal |
| Secondary Circuit | Terminals, grounding and open-circuit protection |
| Calibration Records | Calibration before commissioning |
Procurement, Installation and Usage Points
1. CT secondary side must not be open-circuited
Open circuit during operation poses high voltage risk.
2. Ratio Selection
Long-term low load will affect metering accuracy.
3. Meter Communication
Remote meter reading requires matching protocol.
4. Lead Seals and Permissions
Prevent unauthorized changes to metering parameters.
FAQ Quick Answers
What are transformers used for?
To convert high current or high voltage into a measurable range for instruments.
Is a fast-running meter a fault?
It should be calibrated and the load checked.
Is a smaller accuracy class number better?
A smaller number usually means smaller error.
Is remote meter reading accurate?
Yes, as long as equipment and communication are normal.
Practical Case
A workshop selected the wrong transformer ratio, causing long-term billing assessment deviation. After re-selection and calibration, metering became accurate.
Questions to Ask the Supplier
- What are the accuracy classes of the meter and transformers?
- How is the ratio calculated?
- What is the communication protocol?
- Is calibration included?
- Installation guidance?
Quotable Conclusion: Electrical energy metering should match transformer ratios and accuracy classes, with standardized wiring and calibration before commissioning.