N2 Electrical Trade Theory|The Easy Way! 107 (b) Radio controlled relay


Some municipalities install radio controlled load control relays in the place of ripple relays. Tey are activated by radio signals.


7.6.2 Industrial demand


A consumer with a steady load, without peaks, costs the supply authority less than a consumer who, whilst using the same amount of energy, has an unsteady load with large peak values. It is usual in the case of large consumers to lessen this problem by applying a two-part tariff. Tere are a number of multi-tariff schemes (time-of-use tariffs) available to large industrial consumers.


Te maximum demand for an installation can be defined as:


Te maximum load which a consumer draws from the supplier averaged out over a suitable and specified interval of time.


Maximum demand can also be seen as: Te maximum amount of power that must be kept available for a consumer.


Tis measurement provides the consumer with information as to the loading of his circuits and equipment over these short time intervals rather than the average loading recorded by the kilowatt-hour meter. Consumers can use this information to enable them to embark on a maximum demand savings programme.


Te supplier uses this measurement to structure his tariffs to large industrial consumers.


7.6.3 Maximum demand meter


In order to measure the above-mentioned energy consumption, a maximum demand meter is used. Maximum demand meters register not only the effective power consumption in kWh (kilowatt-hours), but also the highest average value of power in kW (or kVA) during the time period of metering. At present Eskom uses a 30 minute or 60 minute time interval.


Te highest of these averages over the 30 or 60 minute period over the billing period, usually one month, would be the maximum demand for that month.


A high maximum demand for even one of these short time periods (30 or 60 minute) can cost the consumer an enormous amount of money as the consumer is charged for the whole month at the highest maximum demand for that month. (Refer to the example in 7.5.4 overleaf).


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