Load Limiting for Energy Meters

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Many regions in the world suffer from a lag in power supply. The traditional method to supply all customer with electrical power is load shedding. To avoid a complete black-out, parts of the distribution system are shut down deliberately and with given outage times.
Means, the consumer has electrical power for e.g. two hours and no power for the next two hours.

Electronic energy meters with a build-in load switch can be programmed for a maximum load. If a consumer exceeds the limit, he will be disconnected.

Basically it works like this:

Energy Meter Load Limit Function
Energy Meter Load Limit Function

The energy meter makes a permanent comparison of the actual power versus the programmed maximum power. If the actual power is larger than the programmed value a timer is started (timer 1).
The timer values can be chosen by the utility. Usually it’s a duration between 30 s and one minute. If the actual power consumption is still higher than the allowed maximum power, the load switch disconnects.
The load is reconnected after the elapsed time of timer 2.
In the meantime the consumer has the possibility to switch-off some home appliances to reduce the required power. Once the relay has connected, the loop starts over again.

The maximum load can be programmed on-site or by remote connection. The best way is to program remote via an AMI system. Here you can adjust the limits individually for each meter under various aspects like household-size.
You also get a better picture about the demand in certain regions. With increasing generator capacity you can easily set higher limits for all customers.

STS meters

For STS prepayment meters the load limiting is already implemented for a long time. The load limit can be set with a “Set Maximum Power Load Token”. The procedure here is slightly different:
The meter disconnects after 30 seconds (timer 1) and reconnects after two minutes (timer 2). After four disconnection events within 30 minutes the meter remains disconnected for a lockout period of 30 minutes (default).

Display Indication

Over Power Indication
Over Power Indication


If the meter has disconnected due to over-power, the display shows the related information and toggles every two seconds to show the remaining waiting time.

Conclusion

I read recently that smart meters have only a load relay because the utilities are too lazy to go on site for meter disconnection. This is not the case.
Load relays have various functions for protection, tamper disconnection and to serve the utility customer for permanent power.

Thank you for reading.
What is your experience with load limiting?
Comments are welcome.

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