Operator's Manual

ASCO 336 / 337 Operator’s Manual
Page 10 ASCO Power Technologies 381333-427 A
Load Bus Ready for First Generator
CTBx: 11,12, First CTTS Close Enable
If it is possible that the connected load would exceed the
capacity of first gen, it is necessary to open the load ATSs or
CBs before the first gen could come on the bus.
Once any generator starts, generator AC power is available
from the AC Control Power Selector Circuit for this purpose,
but the 336 or 337 CTTS main power contacts may not be
closed until this load is off the load bus, else it will trip
immediately on overload. Interlock contacts will need to be
connected from the load device(s) to all the controllers. This is
a contact input, wetted by internal 24VDC (interrogation
voltage) from the controller power. Conducting means the
load is below the capacity of that generator and it is ok to
bring that generator on the bus. All generators will start, but
none will energize the bus if this contact is open on all of
them. Do not parallel contact inputs from different controllers
together: the system could be damaged. Separate contacts
must be wired to each controller. Separate contacts are used
because it is possible to have different size generators. Once
the first generator is on the load bus, this contact is ignored
and the other generators parallel normally to share the load.
Neutral or Ground current CT
If the power system is 3 phase 4 wire, the fourth CT input is
designed to measure the neutral current. If the power system 3
phase 3 wire, this input may be used to measure ground
current. It is critical the power system grounding is connected
correctly for this current, neutral or ground, to be measured
properly. See drawings for details.
AC Control Power Selector Circuit
and the Loss of AC Control Power
The generated voltage is available from the AC Control Power
Selector Circuit (fused at 20A) before the primary power
contacts close. This AC power could be used to operate load
ATSs or other system requirements. It is also used to open
any CTTS contacts left closed by unintentional or emergency
operations.
Loss of AC Control Power is not necessarily a fatal error: the
control system monitors AC Control Power and can take other
actions if a trip is needed. See Protective Relaying Functions.
The generator circuit breakers are normally closed so AC
Control Power is available from the line (generator) side of
both halves of the CTTS before the main power contacts close.
The AC Control Power Selector Circuit provides AC power
from either of the 2 generators (any one of the gens in a 4 gen
system). The voltage of this AC Control Power Selector
Circuit will be the system phase-to-phase voltage. If several
load ATSs are to be operated, it might be necessary to stagger
their operation to prevent blowing the control power fuse.
In a 336, one Source Selector Relay (SSR1) will switch AC
control power from either Gen1 OR Gen2. In a 4 gen system,
SSR1 in the 337 will switch between Gen3 and Gen4. The
output of the 2 SSR relays, 1 in the 336 and the other in the
337, will feed SSR2 in the 337. In Boolean logic terms, SSR2
switches [(Gen1 OR Gen2) OR (Gen3 OR Gen4)]. Thus if any
generator is running, AC Control Power will be available to
all.
There could be several different sources of AC
Control Power in the system. If any generator is
running, there will be potentially lethal voltages in
every section.
Loss of AC will be detected by the controller, alarmed, and
indicated on the controller. Each controller will detect its own
generator AC power and pass this information to the other
controllers via internal communications link, thus if any gen is
on, all controllers will know the status of the AC Control
Power.
WARNING
!