Handbook of Electrical Engineering

ESTIMATION OF PLANT ELECTRICAL LOAD 15

1.7.1 The key single line diagram

Switchboards and motor control centres:

• All switchboards and motor control centre names, bus-section numbers, line voltages, number of
  phases, number of wires, frequency, busbar continuous current rating.


• Identification of main incoming, bus-section, outgoing and interconnecting circuit breakers, includ-
  ing spare and unequipped cubicles.


• Some diagrams show the cable tag number of the principal cables.

Generators:

• Names and tag numbers.


• Nominal ratings in MVA or kVA and power factor.


• D-axis synchronous reactance in per-unit.


• D-axis transient reactance in per-unit.


• D-axis sub-transient reactance in per-unit.


• Neutral earthing arrangements, e.g. solid, with a neutral earthing resistance (NER), with a common
  busbar, switches or circuit breakers for isolation.


• Current and time rating of the NER if used, and the voltage ratio of the earthing transformer
  if used.

Transformer feeders:

• Names and tag numbers.


• Nominal ratings in MVA or kVA.


• Leakage impedance in per-unit.


• Symbolic winding arrangement of the primary and secondary.


• Line voltage ratio.

High voltage and large low voltage motors:

• Names and tag numbers.


• Nominal ratings in kW.

General notes column or box:

Usually several notes are added to the diagram to explain unusual or particular features, such as
interlocking, limitations on impedance values for fault currents or voltdrop.

1.7.2 Individual switchboards and motor control centres

• Switchboards and motor control centre name and tag number.


• Bus-section numbers or letters.


• Cubicle numbers or letters.