We can find three items in most corporate electricity bills:
- Consumption of active energy (kW·h)
- Power factor consumption (kvar·h)
- Power rating, contracted power or Maximum demand.
The maximum demand is the power accumulated during a determined period, usually between 8 and 30 minutes.
The most common period in most countries is 15 minutes, in Malaysia it is 30 minutes. The power is calculated by the maximeter, which records the greatest value in a month, which is the month billed.
There are three different ways of calculating the maximum demand:
1. Fixed Window
The power utility company provides an impulse during each period to synchronize the start of the maximum demand period.
2. Sliding Window
There are no synchronization impulses, so that the last 15 minutes are used (in the case of 15 min periods). The value is updated with the last 15 minutes each second.
3. Time Synchronisation Window
This is a variation of the fixed window. The power utility company provides the synchronization impulse at the start of the day, which indicates the start of the first period. During the rest of the day, the synchronization for each period will be provided by the unit’s clock instead of the electrical company. A new impulse will be sent by the company at the end of the day, in order to re-adjust the unit’s clock with the company’s clock.