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THREE-PHASE ASYNCHRONOUS MOTORS WITH SLIP RING ROTOR
OUR SLIPRING MOTOR SUPPLY IS DIVIDED INTO TWO SECTIONS
VEM MOTORS GmbH AEM DESSAU GmbH
FRAME 132 - 315 FRAME 355 - 500
LOW VOLTAGE LOW AND MEDIUM VOLTAGE
4-10 POLE 2-12 POLE
VARIOUS DUTY CYCLES VARIOUS DUTY CYCLES
SLIPRING MOTOR EXPLAINED
o The slipring or wound rotor motor is an induction machine where the rotor comprises a set of coils that are terminated in slip rings to which external impedances can be connected
o The stator is the same as is used with a standard squirrel cage motor
o By changing the impedance connected to the rotor circuit, the speed/current and speed/torque curves can be altered
o Slipring motors are switched through their rotor circuit by inserting suitable resistances and then removing them gradually
o Motor torque is directly proportional to external resistanceo Motor starting current is inversely proportional to the external
resistance
APPLICATIONS
o Because a slip ring motor is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range, slipring motors are best utilised (but not limited to) the following applications:
o Overhead cranes and hoistso Crushers o Mill applicationso Mixers
ADVANTAGES OF A SLIPRING MOTOR
o High start-up torque
o Low starting current
o Minimal heat build-up on rotor (as heat is dissipated via external resistors )
o Can be stopped & started more often than a conventional induction motor
SLIPRING MOTOR INDUCTION MOTORThe torque and power input may be varied in small increments during the start-up, as well as within wide limits, by varying the resistor steps inside the starter
The build of the rotor defines the torque curve during start-up, which cannot be varied
By switching on a starter resistor in any phase of the rotor winding, the start-up torque can be changed. In fact the start-up torque can be increased up to the breakdown torque by the very choice of resistor. The start-up resistor is reduced as the supply voltage is applied during start-up and is eventually short-circuited.
When turned on directly, the motor will start up according to its torque characteristic, the start-up current being a multiple (normally four to seven times) of the nominal current, depending on the speed of the motor and power output.
The size of the starter, the number of tapping positions and the definition of the tap resistors, orient themselves to the inertia of the starting duty and to the starting frequency.
The fundamental mode of the motor voltage isadjusted via phase control of varying degree, and thus via torque and starting current.
During start-up the voltage drops down to a value proportionate to the load. If the power supply lacks the required capacity, another starting method must be chosen.
COMPARISON
VEM SLIPRING RANGE
• VEM manufacture slipring motors as per customer specifications
• Duty cycles are S1 continuous rated to S4/S5 short rated (typically designed for crane application)
• In the case of a replacement motor your existing bearing, shaft and design arrangement is fully accommodated by VEM
A typical schematic showing the external resistors in circuit
PHYSICAL ADDRESS POSTAL ADDRESS
28 BELL STREET P.O.BOX 15300MEADOWDALE EXT.1 HURLYVALEROUTE 24 1611GERMISTON SOUTH AFRICA
CONTACT INFORMATION
TEL: 011 974 8487FAX: 011 974 9704EMAIL: [email protected]: www.emac-online.com
SALES CONTACTS
Mr. PETER MARTIN 082 653 6285 [email protected]. CLINTON WADELEY 082 654 7700 [email protected]. BRADLEY MEYER 082 327 7815 [email protected]
