Shunt

[treyp3]

What exactly is a shunt? I dont know what a shunt feild in a generator is, or how a shunt breaker works. Anyone have a good explanation, also, I'm looking for a good web site that goes into detail on this issue.

 

[iwire]

I can't help with the generator but a shunt breaker is usually just a normal breaker with a magnet coil added that when energized causes the breaker to immediately trip off regardless of the load on the breaker.

We use them a lot to shut equipment off under cooking hoods.

 

[stew]

The shunt fields in a generator is the field wound with several turns of fine wire that is used to control the output in a compound generator. Compound generators have 3 sets of field windings. The series fields are the large heavy windings that carry the output current. The Interpole windings help reduce arcing at the brushes and kind of smooth out the output. The shunt fileds are normally powered by an external exciter winding and the intensity of the magnetization of those fields is controlled by a rheostat. The shunts contol the output of the generator. At least thats how a dc generator welder works.

 

[stew]

some other applications of shunt breakers that I have seen are on gas station emergency shut off swithches and elevator emergency stop buttons.

 

[treyp3]

Thanx for the help guys. Got the breaker part, but would like to see a diagram for the shunt field of a motor. Will search the net when I have more time, but please let me know if you know a good web site for the inner workings of motors ie exciter, balancer set, shunt field. Would like to know more.

 

[jim dungar]

Again slang rears its ugly head.
The others are describing shunt trip breakers.

In general terms a shunt is a bypass device, but remember generalities due not apply everywhere.

A shunt trip is a separately energized coil that bypasses the normal tripping mechanism.
A shunt winding is a winding separate from the main power windings
A metering shunt is a precision resistor, a voltmeter meter can then be used to measure the voltage drop which is proportional to the current in the circuit.
A fusible shunt is solid conductor used in place of a protective fuse.

 

[gar]

110602-1202 EDT

treyp3:

From dictionary.com

Electricity .
a. to divert (a part of a current) by connecting a circuit element in parallel with another.
b. to place or furnish with a shunt.

In the case of a shunt used to measure current it is a calibrated low resistance resistor placed in parallel with an ammeter or low voltage voltmeter. A 50 millivolt 10 A shunt would have a resistance of Rs = 0.050 / 10 = 0.005 ohms. This is the resistance between the two terminals that the voltmeter is connected across. Suppose the voltmeter required 1 A of current, then the shunt resistance would actually be 0.050 / 9 = 0.005555556 ohms and would be a special shunt. For a picture of a 4 terminal shunt see photo P-19 at my web site http://beta-a2.com/EE-photos.html .

A shunt field DC motor or generator has the fixed magnetic field supplied by a wound coil in parallel with the armature voltage. Conventional construction has the field stationary and the armature with commutator rotates. If it is a motor, then the voltage applied to the armature is also applied to the shunt field. So long as the applied armature voltage is constant, then so is the field excitation also constant. If two different supplies are used, one for the field and the other for the armature, then technically the motor would not be a shunt wound anymore, but a separately excited field. Yet the motor has not really changed.

A variation of the shunt field motor is a compound motor (same applies to a generator and I believe Edison and his people invented this to provide constant voltage output under varying load). In the compound motor there is a second coil in the field magnetic circuit. In a DC motor with fixed field excitation the output speed decreases approximately linearly with increasing load. Armature current is proportional to load torque. If the second field coil is in series with the armature, then a motor can be made to have nearly constant output speed with varying load.

Another type of DC motor is the strictly series type and this has substantially different characteristics.

.

 

[gar]

110602-1318 EDT

A couple references:

http://en.wikipedia.org/wiki/Brushed_DC_electric_motor
http://zone.ni.com/devzone/cda/ph/p/id/54

.

 

[stew]

The shunt winding in a compund generator or a compound motor is used to control either output in the case of a generator or speed in the case of a motor.

 

[beanland]

Shunt & Series

Shunt & Series

Easier: a shunt is a parallel connection to the system in contrast where a series is just that. Series winding is in series with the rotor but a shunt is in parallel with it; a shunt trip breaker has a trip coil in parallel with the overcurrent element in the breaker; a shunt capacitor/reactor is connected in parallel with the load where a series capacitor/reactor is in line with the load.

 

[richxtlc]

In addition to all the above, in the utility field, a shunt is a temporary feed to a customer, usually above ground, until a new service can be installed underground.