Training Manual on Energy Efficiency - APO Asian Productivity ...

5. ELECTRICAL LOAD MANAGEMENT
5.1 INTRODUCTION
In industrial type electricity billing, where mostly a two-part tariff is adopted,
the consumer pays for two components:
• For the maximum demand (kVA) recorded during billing duration; and
• For the energy (kWh) consumed during billing duration.
Electrical load management for a company involves measures to reduce
maximum demand and to improve power factors so that the maximum
demand charges are minimized. Energy consumption mainly relates to end-use
equipment efficiency and can be reduced by various relevant measures.
5.2 MAXIMUM DEMAND BASICS
Maximum demand charges relate to the fixed cost of capacity blocked to be
provided for serving a consumer’s needs.
A tri-vector meter installed at the consumer end records the maximum
demand registered by a consumer during billing duration, apart from other
important consumption features like active power (kWh), reactive power
(kVarh), apparent power (kVah), and power factor (PF).
At present many utilities have a “time of day tariff” in place, and charge a
consumer variable rates for maximum demand drawn during different times
of day. For instance, there could be lower rates for night hours when the
utility is lightly loaded and higher rates during evening hours when utilities
are stretched to meet maximum load demands. It would thus help to study
the load curve patterns and, based on prevalent tariff structure provisions,
optimize maximum demand to save on maximum demand charges.
5.2.1 Load curve of a plant
From Figure 5-1, one can see that demand varies from time to time, due to
the combination of users and consumption of electricity changing all the time.
The demand is measured over a predetermined time interval and averaged out
for the interval as shown by the horizontal dotted line.
- 47 -