Brochures and Data Sheets

Product Features
• Open or closed transition transfer between normal and emergency.
• Emergency or peak shave mode of operation.
• Engine start control logic and load control logic.
• Available configurations include either an ASCO 434, 436 or ASCO’s new
7000 Series closed transition transfer switches through 4000 amperes. The
transfer system configuration can also accommodate power circuit breakers.
• Normal and emergency circuit breakers can be provided when using a
transfer switch for overcurrent protection.
• Full manual paralleling operation (standard).
• Protective relaying (as required).
• Optional instrument meters for normal, emergency, or load for
local monitoring.
• Designs are based on NEMA and UL 891 standards.
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Soft Load Transfer System
ASCO soft load closed transition transfer switches provide a make-before-
break transfer of a building load from a utility power source to an alternate
power source. This system automatically brings the engine generator into
synchronism with the utility source, then gradually shifts the load from the
utility to the engine generator with virtually no voltage or frequency
fluctuations.
Figure 13 shows a typical soft load transfer system containing an ASCO closed
transition transfer switch.
Fig. 14 One line diagram of the soft load transfer
system shown in figure 13.
CTTS
KW
V
A
F
KW
32R
86
25C
90*
65*
43
V
47N
27
59
81
O/U
43
43
ASCO
Control Panel
Load
Alternate
Power
Source
Utility
Power
Source
Watt
XDCR
To 52G
Shunt Trip
SY
Ground 400A
Neutral 2000A
Phase 2000A
STB
STB
STB
V - Voltmeter
A - Ammeter
F - Frequency Meter
KW - Wattmeter
Watt XDCR - Watt Transducer
STB - Shorting Terminal Block
25C - Synch Check Relay
27/59 - Under/Over Voltage Relay
32R - Reverse Power Relay
47N - Phase Sequence Under
Voltage Relay
65 - Governor (*)
81O/U - Over/Under
Frequency Relay
90 - Voltage Regulator (*)
CTTS - Closed Transition
Transfer Switch
SY - Synchroscope
43 - Phase Selector Switch
86 - Lockout Relay
Note: * Furnished by
alternate power
source supplier
Fig. 13 Soft load transfer system.