Thermal Overload Protection Formula

In either case the presence of thermal overload can be detected and removed before cable failure occurs.

Thermal overload protection formula.

R r θ dt dθ r r 1 s i c m r 2 8 s τ c m r 9 let r r u θ 10 and dt d r r 1 dt du θ 11 therefore the first order thermal model equation becomes the simple form. This is the principle behind the thermal replica model of a motor used for overload protection. 40 ec and service factor. Calculated sizing for overload device to provide overload protection to a 3 phase 200 volt 15 hp motor with full load ampere is 35 ampere ambient temp.

There is one cylindrical stator and a three phase winding is symmetrically distributed in the inner periphery of the stator. Due to such symmetrical distribution when three phase power supply. τ t. If the motor in the example from step 2 had a service factor of 1 15 then its overload would be acceptable and the motor could be operated without damage.

35 ampere x 125 43 7 ampere 44 ampere. Therefore this type of relay is used in conjunction with fuses to provide overload and short circuit protection to the circuit. Tmax final steady state temperature τ heating time constant. U dt du i2 τ 12 the solution of the first order equation is.

Electric motors are commonly rated for operation in an ambient temperature of 40 deg. Temperature rise is proportional to the current squared. The temperature t at any instant is given by. Answer ambient temp 40 ec.

Thermal overload protection is normally used in an alarm mode to notify system operators of the potential for cable damage. The fundamental equation 6 can be expressed in a simpler form. For understanding motor thermal overload protection in induction motor we can discuss the operating principle of three phase induction motor. 1 ib in iz ib anticipated operating current of the circuit iz current carrying capacity of conductor or cable or motor.

Check the motor nameplate for the ambient temperature rating and the insulation class ratings. However thermal overload protection can be used to trip a circuit breaker as well. C 104 deg.