Energiatarbimise juhtimine
Power loading of an installation
Argo Rosin
Installed power loads - Induction motors
The full-load current Ia supplied to the motor is given by
the following formulae:
3-phase motor: Ia = Pn x 1,000 / (√3 x U x η x cos ϕ)
1-phase motor: Ia = Pn x 1,000 / (U x η x cos ϕ)
where
Ia: current demand (in amps)
Pn: nominal power (in kW)
U: voltage between phases for 3-phase motors and
voltage between the terminals for single-phase motors
(in volts). A single-phase motor may be connected
phase-toneutral or phase-to-phase.
η: per-unit efficiency, i.e. output kW / input kW
cos ϕ: power factor, i.e. kW input / kVA input
Installed power loads - Induction motors
The current supplied to the motor, after powerfactor correction, is given by:
where cos ϕ is the power factor before
compensation and cos ϕ’ is the power factor
after compensation, Ia being the original current.
Installed power loads –
Resistive-type heating appliances and
incandescent lamps (conventional or halogen)
Fluorescent lamps and related equipment
Standard tubular fluorescent lamps
Installed apparent power (näivvõimsus)
η = the per-unit efficiency = output kW / input kW
cos ϕ = the power factor = kW / kVA
The apparent-power kVA demand of the load Pa = Pn /(η
x cos ϕ)
The full-load current for single phase-to-neutral
connected load
The full-load current for three-phase balanced load
where:
V = phase-to-neutral voltage (volts)
U = phase-to-phase voltage (volts)
In normal operating conditions the power consumption of
a load is sometimes less than that indicated as its
nominal power rating, a fairly common occurrence that
justifies the application of an utilization factor (ku) in the
estimation of realistic values.
It is a matter of common experience that the
simultaneous operation of all installed loads of a given
installation never occurs in practice, i.e. there is always
some degree of diversity and this fact is taken into
account for estimating purposes by the use of a
simultaneity factor (ks).
Factor of simultaneity for an apartment block
Factor of simultaneity for distribution boards
Factor of simultaneity according to circuit
function
An example in estimating the maximum predicted
loading of an installation
Choice of transformer rating