General Electrical Terms
1. The Siemens (symbolized S) is the Standard International (SI) unit of electrical conductance.
The archaic term for this unit is the mho (ohm spelled backwards).
2. Type 1 coordination - No damage to person or installation.
However destruction of contactor and OLPD is permissible. Before restarting, the combination the components may need to be repaired / replaced.
3. Type 2 coordination - No damage to person or installation. OLPD may not suffer any damage. Welding of contacts,
with easy separation by screw driver is permissible. Before restarting simple check of combination is required.
4. SFU protects system from Short Circuit Fault.
5. MPCB trips on Overload faults & Short-circuit faults.
6. Star Delta Starter is the simplest form of reduced voltage starting where Starting current is reduced by 1/3 of DOL value
7. Full form of DOL Starter is Direct On Line Starter.
8. To improve power factor capacitor banks are used.
9. RCCB is the safest device to detect and trip on leakage currents and thereby offer instant protection against electrocution and electrical fire.
10. Over-current means current exceeding the rated current
11. Overload means Operating conditions in an electrically undamaged circuit which cause an over-current
12. Harmonics - These are voltage and current frequencies riding on top of normal sinusoidal waveforms.
These are caused due to non linear loads in the power system. Loads like Arc Furnaces, VFDs, Switch Mode Power Supplies, Computers etc contribute to the production of harmonics.
13. Effect of harmonics: Power Loss, Heating & wave distortion. Triplen harmonic especially the 3rd harmonic causes N-Overload & telephonic interference.
14. Full form of IP is Ingress Protection, where in IP Rating (IP XY) First Number X - protection against ingress of solid objects & Second number Y - protection against ingress of water.
15. Standards for Energy Efficient motor is IS:12615 / IEC:60034-1.
16. Forced cooling method (IC416) is used in motors when operated through VFD at very low speeds.
17. VPI treatment will be done to motors when operated through VFD.
18. Efficiency classes of the motor are IE1, IE2, IE3 and IE4.
19. Insulated bearing are using to prevent bearing damage due to bearing currents.
20. Power Contactors Utilization Category.
AC AC1 Non inductive / Slightly inductive loads
AC2 Slip ring motors - starting & switching off
AC3 Squirrel cage motors - starting & switching off
AC4 Squirrel cage motors - starting, plugging, inching
AC5a Switching electric discharge lamps
AC5b Switching incandescent lamps
AC6a Switching Transformers
AC6b Switching Capacitors banks
AC7 Switching inductive loads / motors for household application
AC8 Switching hermetic refrigerant compressors
21. Auxiliary contactor Utilization Categories.
AC AC12 Control of resistive/solid state loads
AC13 Control of solid state loads with transformer isolation
AC14 Control of small electromagnetic loads (£72VA)
AC15 Control of electromagnetic loads (³72VA)
Duty Types of Motors:
Duty :Load the motor is subjected to comprising one or more loads which remain constant for
a specified period or intermittent load in which speed varies intermittently.
S1 - Constant load for a long time such that motor reaches steady temperature.
S2 - Short time constant load.
S3 - Intermittent periodic duty such that starting current does not significantly affect T.R. of motor.
S4 - Same as above but starting current affects significantly T.R. of motor.
S5 - Period of starting ® op. at constant load ® rapid elect. braking ® rest ® de-energised.
S6 - Cycle of constant load + period at no load.
S7 - Period of starting + op. at constant load + rapid electric braking - no rest.
S8 - Period of constant load ® at one speed ® other constant loads at other speeds
No rest, no de-energised period.
S9 - Duty in which load and speed vary non-periodically.
C.D.F. - Cyclic Duty Factor
® total time which contributes to elect. heating (in 1 cycle) x 100% one complete cycle time