Motors, Starters & Variable Frequency

Front 1

Three-phase mutli-lead motors

Back 1

·Single-voltage motors have a stator that has three windings or three groups of windings

·Dual-voltage motors have six windings or groups of winding; two windings or groups for each phase (connected in series for 460V or parallel 230V)

Front 2

Single-voltage motors.

Back 2

·Have six leads.

·Grouped T1&T4, T2&T5, T3&T6

·T1,T2 and T3 are winding starts

·T4,T5 and T6 are winding finishes

·IEC labels U, V and W

·T4,T5 & T6 not brought to connection box U1|T1 V1|T2 W1|T3

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U2|T4 V2|T5 W2|T6

Front 3

Dual-voltage motors

Back 3

·Have 12 leads.

·Only T1-T9 are brought out to connection box

·T10, T11 & T12 remain in the stator

·Dual-voltage 3phase, single speed motors are labeled 230V/460V on the nameplate

·Nine-lead wye motor

·Nine-lead delta motor

Front 4

Nine-lead 230/460V Wye connections

Back 4

Front 5

Nine-lead 230/460V Delta connections

Back 5

Front 6

For both Wye & Delta connections

Back 6

The winding connections are connected in parallel for low-voltage and series for high-voltage

Front 7

Motor direction of rotation

Back 7

·Interchanging any two supply leads changes the direction of rotation of a 3-phase motor

·T1, T2 & T3 connected to lines whose phase sequance is L1, L2 & L3 (ABC) counter-clockwise

·T1,T2 & T3 connected to lines whose phase sequance is L3, L2 & L1 (CBA) clockwise

Front 8

Motor Starters

Back 8

Can be either:

·Across-the-line starters (apply full voltage to the motor at start)

·Reduced-voltage starters (provide reduced voltage at start & full voltage at run)

Front 9

Across-the-line (full voltage) starters

Back 9

·Across-the-line produces starting current that is 500% - 600% of the full load current

·And starting torque that is 150% of the full load torque

Front 10

Across-the-line (full voltage) starters

Back 10

·Across-the-line connects the motor leads directly across the supply

Style of starter may be:

·Manual (open/close switch)

·Magnetic (electrically operated switch - contactor)

·CEC requires a manual disconnecting means on the line side of the magnetic motor starter in the circuit

Front 11

Part-Winding Starters & Motors (Across the line)

Back 11

·This type of starter is for loads with small to no load at start

·If full load is present, the motor could be damaged if the starter does not energize both windings within 2 seconds

·Six conductors required between the starter & motor (the leads are T1, T2, T3, T7, T8, & T9)

·reduces starting torque more than it reduces starting current

Front 12

Part-Winding Starters & Motors (Across the line)

Back 12

Reduced to 60-65% of the inrush current (if both windings were energized at the same time)

Front 13

Reduced-Voltage Starters

Back 13

·Used when the high starting current of a motor can cause excessive volt drop or volt sag (lights dim)

·Reduces inrush starting current

·Reduces starting torque (can be a problem if too much mechanical load on shaft)

·Smoother acceleration & quieter starts

·May require timing relays in the control circuit

Front 14

Timing Relays

Back 14

·Time delay on energization (TDOE) aka On-delay relay occurs after the relay coil is energized

·Time delay on de-energization (TDOD) aka Off-delay occurs after the relay coil is de-energized

·TO (timed to open)

·TC (timed to close)

·Contact moves in direction of arrow after timing is complete

Front 15

Autotransformer Starters Calculations

Back 15

Starting voltage of the motor (Vrv) is proportional to starting current of the motor (Im)

384 Vrv

4.8 = ------

80 A (motor)

Starting voltage (VFv) is proportional to the line current (IL)

480 VFv

4.8 = ------

64 A (line)

Front 16

Autotransformer Starters Calculations

Back 16

·Apparent power of motor:

S = V (at motor) × I (at motor)

·Autotransformers can have 80%, 65%, or 50% taps

·Line current calculation:

(384)2

(Starting current)-->100A × (------)

(480)

·80% tap, plus squared -->.802 = 0.64 <--Starting torque

·Find starting torques by using taps

Front 17

Autotransformer Open & Closed Starter Transitions

Back 17

·Open-transition momentarily disconnect the motor during transition from reduced-voltage to full-voltage

·Open-transition have higher transition currents & higher torque changes (torque bump)

·Closed-transition maintain current to the motor during transition from reduced-voltage to full-voltage

·Closed-transition offers better performance

Front 18

Wye-Delta Starting

Back 18

·The motors three windings (T1 to T6) or groups are connected in Wye for starting, and are reconnected in delta for running