Motor Protection and Its Types of Electrical Faults

There is a wide range of motors in existence for various purposes. However, the fundamental problems affecting the choice of motor protection are independent of the type of motor and the type of load to which it is connected. The motor under discussion here are a.c. motors which include synchronous  and induction motors protection and its types of electrical faults.

 

 

Types of Faults to be protected in Motors

Types of electrical faults in motors are similar to those of generators. Motors therefore in general are protected against the following faults:

1. Stator faults
2. Rotor Faults
3. Overloads
4. Unbalanced supply voltages including single phasing
5. Under voltage
6. Reverse or Open-phase starting
7. Loss of synchronism ( in the case of synchronous motors only)
   

Mho relay | Admittance or Angle Admittance Relay

Mho Relay Construction and principle of Operation

A simple form of Mho relay | Admittance or angle admittance relay shown in the figure below:

 

 

It is an electromagnetic induction cup type mho relay.

The torque equation is given by T = K₁ VI (Φ – α) – K₂V² – K₃

The upper and lower poles are energized by a voltage V to produce a polarizing flux. The capacitor connected in series provides memory action. The left is energized by a current is the operating quantity. The left pole due to current I interacts with the polarized flux due to V produce the operating torque K₁VI Cos (Φ – α).