Aug 17, 2016

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.
Motor Protection

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)

Aug 15, 2016

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:
Induction Cup Type Mho Relay
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).