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Load Limiting Solution Prepared by: Gary Moor, Product Manager Abstract- The frustration facing consumers during South Africa’s energy crisis is the lack of control with regards to their supply continuity. Regulation and control of the supply is in the hands of the utility. Conlog has a solution that now shifts this responsibility of power management to the consumer while still guaranteeing the utility their required load reduction. The consumer is now afforded an opportunity through their own actions as to whether or not they are load shed.

1. INTRODUCTION

Currently, meters produced by Conlog are able to dynamically limit the maximum load that a meter may deliver. If the maximum limit is exceeded, the meter trips (similar concept to the overload feature of a circuit breaker). This is not a new concept and is regularly used in the field. A meter physically able to deliver 100A is often de-rated by entering a simple token to any value (e.g. 5A) as requested by the utility. Tokens can regularly be generated to readjust the maximum load.

Using this concept, meters rolled out to a particular area can receive a signal to reduce their maximum allowable load. This signal can transmit a schedule or in emergency scenarios, a command requesting immediate action. Once the meter receives the signal, it alerts the consumer of this pending degradation in available power. Reducing consumption is now the consumer’s prerogative; he has control over whether or not to be load shed. The consumer disconnects unessential appliances until such time that the combined loading on the meter is within the new limit (indicated by the meter).

Failure to comply with the request within the prescribed time to remove some of their loads now results in the individual being disconnected. The consumer can still reconnect themselves but only by disconnecting some nonessential appliances until they are within the permissible load.

The utility is now in the advantageous position of being able to shift responsibility of reducing consumption off themselves and onto the consumer. It’s the consumer’s lack of control over their supply to which they are entitled, that has compounded their frustrations. The utility no longer needs to load shed complete regions in order to reduce consumption but can merely downgrade those consumers maximum usage. The utility still honours its obligation in providing electricity to the consumer. The difference is that now the supply is capped.

It must be kept in mind that this proposal is not a prepayment solution as does not require prepayment architecture. The meters used can be prepayment (although prepayment has proven to reduce average loading by up to 20%), post payment, or even merely a load limit device.

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2. TRANSMISSION

Conlog’s current AMR (Advanced Meter Reader) technology allows one to remotely access up to 24 “split” meters using the GSM network (Drive-by and ripple control are also possible). A split meter is one where the metering part of the unit is kept separate from the interface unit which the user has access to. The user uses the interface unit (UIU) to enter tokens and request certain information from the meter. This UIU is currently connected to and powered by the meter through a split core wire. The AMR unit acts as a concentrator, connecting up to 24 meters via these communication connectors to a centralised unit. The concentrator is able to process commands to and from the connected meters and communicate with the management system via its GSM modem. All the meter’s features are now available from any remote location via the GSM network (GPRS/ SMS). This in effect allows the utility access to the meter from a centralised point. Adjusting the maximum load, downloading load profiles, analysing the quality of supply, uploading credit tokens (prepayment) and tamper status are some of the many features available remotely.

3. WIRELESS

The solution described has a drawback in that it requires a wired communication link between the meter and UIU and between the meter and AMR concentrator. These physical limitations confine this solution to smaller footprints per concentrator. Installation is also very labour intensive and costly. Access to the customer’s premises is also required and intrusive installation of the UIU and sometimes the meter, guarantees the public’s general disapproval, which has been evident in current geyser switch installations.

Conlog has a wireless UIU solution which is currently awaiting validation. A RF (Radio Frequency) unit is added to the existing meter via the communication terminals and provides wireless communication to a new wireless UIU. Thus a physical cable connection is no longer required between the meter (generally installed externally to the consumer’s premises) and the UIU.

A basic AMR concentrator has been developed within our research facility with wireless connectivity to these new wireless meters. This prototype wireless AMR concentrator (still in its developmental stage) can now function as the wired solution before it, but now through wireless connects up to 255 meters within its radio range to the GSM network. This obviously hugely reduces the communications cost to the meters. This bidirectional communication also provides many of the “smart metering” solutions that have been too expensive to previously justify.

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4. LOAD SWITCHES

Now that the onus is on the consumer to manage their load, a couple of scenarios exist whereby the consumer might not hear the load limit notification (e.g. not at home) and might not be in a position to disconnect his appliances. In these cases, it would be beneficial for the meter to automatically disconnect loads.

A solution to this scenario exists with a wireless automatic load disconnection device. This is unlike the current concept of a load disconnection device in that it is beneficial for the consumer to have; people won’t be trying to bypass them and will actually want to install them because of the convenience that they provide.

The load switches can be installed onto any nonessential appliance in the homestead. The best utilisation would be to install them on heavier loads, for example water heaters, pool pumps, air cons etc. The idea is that once a signal to load limit is received, the meter will signal the load switches to disconnect their various loads, thus dropping the combined loading to within a safe margin of consumption.

This load disconnection procedure is evolved to an intelligent state where the meter is preloaded with a prioritised order of disconnection. Thus when the load limit signal is received, the loads are disconnected in a sequence until the combined loading is deemed safe.

The utility has fulfilled its responsibility of providing power and so the onus will be on the consumer to purchase these RF load switches from a retail store (Game, Makro etc.). Pairing the load switch to the meter at home is simple process and each device is uniquely paired.

A random reconnect feature is currently used in all Conlog’s meters but this could be extended to load switches. This random reconnection of loads reduces the impact on the network during reconnections.

5. CONCLUSION

This current energy crisis is not going to be solved in the next few years. More generation is required but Conlog’s solution now provides a means by which small industry and residential consumers can be tasked to better manage their loads. Most of the units discussed are available but some changes are required to have a complete solution that better addresses the requirement.