Klockner Moeller Electric Parts from KlocknerMoeller.net
|
 |
Call Toll Free!
1-877-595-9616
|
|
Largest Authorized Stocking USA Distributor
Representing
|
| |
Contactors and Relays
Overload relays Z |
| |
| Motor protection using Z thermal
overload relays |
| |
Overload relays are included in the group of
current-dependent protective devices. They monitor the temperature of
the motor winding indirectly via the current flowing in the supply
cables, and offer proven and cost-efficient protection from destruction
as a result of:
- Non starting
- Overload
- Phase-failure
|
Overload relays operate by using the characteristic
changes of shape and state of the bimetal when subjected to heating.
When a specific temperature is reached, they operate an auxiliary
contact. The heating is caused by resistances through which the motor
current flows. The equilibrium between the reference and actual value
occurs at various temperatures depending on the magnitude of the
current.
Tripping occurs when the reference temperature is reached. The tripping
delay depends on the magnitude of the current and preloading of the
relay. Whatever the current, the relay must trip out before the motor
insulation is endangered, which is why EN 60947 states maximum response
times. To prevent nuisance tripping, minimum times are also given for
the limit current and locked-rotor current. |
| |
| |
|