Page 197 - HVAC Pump Handbook

Rishel_07.qxd 20/4/06 6:29 PM Page 194

Pump Drivers and Variable-Speed Drives

194 HVAC Pumps and Their Performance

Lin 10 m/Div
Volts
250 m
Noauto
Upper
50 m
/Div
−250 m
0 – – Seconds – – 79.98 m
Off Ch–1/ Time 1 Voltage/
t: os
y: –37. 6 m V
Lin 10 m/Div Motor current
Volts
150 m
Noauto
Lower
50 m
/Div
−150 m
0 – – Seconds – – 79.98 m
Figure 7.10 Output voltage (top) and current of a GTO/SGCT current-fed VFD.
(From Richard H. Osman, Medium–Voltage Variable Frequency Drives for Induction
and Synchronous Motors.)

thyristors cause distortion of the power-line voltage (the infamous
notching), and this distortion may affect equipment in the building or
in neighboring facilities. The problems may become acute when power
factor correction capacitors are installed. The capacitors resonate with
the power-line inductance and may amplify harmonic currents to many

Typical
snubber

3-Phase MV input Induction
motor

Input filter for
harmonic correction
12 Pulse rectifier GTO Neutral-point-clamped inverter
Figure 7.11 GTO/IGCT voltage-fed neutral-point-clamped inverter. (From Richard H.
Osman, Medium–Voltage Variable Frequency Drives for Induction and Synchronous
Motors.)

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