Contact Inputs - GE 850 Instruction Manual

CHAPTER 5: DEVICE, SYSTEM, INPUT AND OUTPUT SETPOINTS

Contact Inputs

NOTE:
NOTE
850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
The 850 relay is equipped with a number of Contact Inputs, depending on the Order Code,
which can be used to provide a variety of functions such as for circuit breaker control,
external trips, blocking of protection elements, etc. Contact inputs accept wet and dry
input signals. A wet type contact input signal requires an external DC voltage source. A dry
type contact input signal uses an internal DC voltage source. Depending on the DC source
level, the voltage threshold (17V, 33V, 84V, 166V) can be selected. The Contact Inputs can be
located on the HV I/O and Arc Flash cards located on slots 'B' or 'C' or 'F' or 'G' or 'H' or all.
The maximum load current that can be delivered by the relay +24 V wetting voltage supply
is 100 mA. When the internal +24 V supply is used, the current limitations of the 24V supply
must be considered.
The Contact Inputs are either open or closed with a programmable debounce time to
prevent false operation from induced voltage. The debounce time is adjustable per
manufacturer specifications.
A raw status is scanned for all Contact Inputs synchronously at the constant rate of one
protection pass (1/8 cycle) as shown in the figure below. The DC input voltage is compared
to a user-settable threshold. A new Contact Input state must be maintained for a user-
configurable debounce time in order for the relay to validate the new contact state. In the
figure below, the debounce time is set at 2.5 ms; thus the 3rd sample in a row validates the
change of state (mark no. 2 in the diagram). Once validated (debounced), the new state will
be declared and a FlexLogic operand will be asserted at the time of a new protection pass.
A time stamp of the first sample in the sequence that validates the new state is used when
logging the change of the Contact Input into the Event Recorder (mark no. 1 in the
diagram).
Protection and control elements, as well as FlexLogic equations and timers, are executed
eight times in a power system cycle. The protection pass duration is controlled by the
frequency tracking mechanism. The FlexLogic operand reflecting the debounced state of
the contact is updated at the protection pass following the debounce (marked no. 2 on the
figure below). The update is performed at the beginning of the protection pass so all
protection and control functions, as well as FlexLogic equations, are fed with the updated
states of the Contact Inputs.
The FlexLogic operand response time to the Contact Input change is related to the
debounce time setting plus up to one protection pass (variable and depending on system
frequency if frequency tracking enabled). For example, 8 protection passes per cycle on a
60 Hz system correspond to a protection pass every 2.1 ms. With a contact debounce time
setting of 3.0 ms, the FlexLogic™ operand-assert time limits are: 4.2 + 0.0 = 4.2 ms and 4.2
+ 2.1 = 6.3 ms. The 4.2 ms is the minimum protection pass period that contains a debounce
time, 3.0 ms.
Regardless of the contact debounce time setting, the Contact Input event is time-stamped
with 1 protection pass accuracy using the time of the first scan corresponding to the new
state (mark no. 1 below). Therefore, the time stamp reflects a change in the DC voltage
across the Contact Input terminals that was not accidental as it was subsequently
validated using the debounce timer. The debounce algorithm is symmetrical: the same
procedure and debounce time are used to filter the LOW-HIGH (marks no.1 and 2 in the
figure below) and HIGH-LOW (marks no. 3 and 4 below) transitions.
INPUTS
5–85