HP Type K02 Посібник користувача - Сторінка 23

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AC Controls

Reduced Voltage Starters — Electromechanical

Auto Transformer Starter

Operation

At starting, the auto transformer reduces

motor terminal voltage to 50, 65, or 80

percent of line voltage. For a timed inter-

val, a segment of the transformer coil is

connected in series (as an inductor) with

the motor. Then a contactor automatically

connects the motor across the line and

shorts out the inductor.

Auto Transformer Starter

Typical Speed Torque Curves

Table 15.35

Comparison of Various Electromechanical Methods

of Reduced Voltage Motor Starting

Characteristics

Starting current drawn from line as % of

that which would be drawn upon full

voltage starting

Starting torque developed as % of that

which would be developed on full

voltage starting

Smoothness of acceleration

Allowable accelerating times (typical)

Closed Transition.

Full voltage start usually draws between 500% and 700% of full load.

Approximate values only. Exact values may be obtained from motor manufacturer.

Solid state starters provide the smoothest starting characteristics.

306

Wye Delta Starter

Operation

Initially the starter connects the motor

on a Wye connection, reducing voltage

across the winding to approximately

58 percent. Starting torque and current

is about 33 percent of across the line.

After a time delay the motor is

connected Delta.

Wye Delta Starter

Reduced Voltage Starting

Autotransformer

Part Winding

50%

65%

80%

Tap

2 Step

25%

42%

64%

Increased slightly with

45%

speed

First in order of

Third in order of

smoothness

30 seconds

2-3 seconds

Based on NEMA

Limited by

medium duty

motor design

transformers

Siemens Electrical Products and Systems

Specification Guide

Part Winding Starter

Operation

Part winding starters apply starting

current in timed steps to part winding

motors. Two step controllers apply volt-

age through one starter to one motor

winding followed by the second starter

which connects voltage to the second

winding. The timer may be adjusted to

automatically close the second controller

at the most favorable time to minimize

voltage fluctuations.

Part Winding Starter

Wye(Star) Delta

33%

Second in order of

smoothness

45-60 seconds

Limited by

motor design

General

CSI Section 16160