# The order of the sub-harmonic during SSR for 50 Hz normal frequency is

The order of the sub-harmonic during SSR for 50 Hz normal frequency is

### Right Answer is:

50/3 HZ

#### SOLUTION

## Sub-synchronous resonance

- The transient currents at the sub-harmonic frequency resulted in a series-compensated network due to a switching operation or a fault.
- These sub-harmonic frequency currents assume dangerously high values and even become unstable.
- The unstable operation is exhibited in the form of negative resistance in the equivalent circuit of synchronous and induction motors.
- Sub-synchronous resonance (SSR) is a phenomenon in which electrical energy is exchanged between generators and transmission systems below the nominal power frequency (50/60Hz).
- Synchronous Resonance (SSR) is a phenomenon in which electrical energy is exchanged between generators and transmission systems below power frequency.
- It can be caused due to interaction of a series compensated transmission line with a generator; in addition, results in oscillation in the shaft and power swing.
**The subsynchronous frequency is typically 1/3 of the fundamental frequency. So for 50 Hz fundamental frequency, the subsynchronous frequency is 50/3 Hz.**