5. Process bus
The process bus utilizing IEC 61850-9-2 LE together with the
IEEE 1588 v2 accurate time synchronization provides sampled
measured values over the Ethernet communication. The
sampled measured values comprise four currents and four
voltages, that is, phase and residual currents as well as phase
and residual voltages. The residual voltage is calculated from
the measured phase voltages. The sample rate is 4000/4800
samples per second depending on the selected system
frequency.
6. Self-supervision
The merging unit’s built-in self-supervision system continuously
monitors the state of the merging unit's hardware and the
operation of the merging unit's software. Any fault or
malfunction detected is used for alerting the operator.
A permanent merging unit fault blocks the application to
prevent incorrect operation.
7. Secondary circuit supervision
Current circuit supervision is used for detecting faults in the
current transformer secondary circuits. Upon detecting a fault,
the current circuit supervision function activates an alarm. The
current circuit supervision function calculates the sum of the
phase currents from the protection cores and compares it to
the measured single reference current from a core balance
current transformer or from separate cores in the phase current
transformers.
The fuse failure supervision detects failures between the
voltage measurement circuit and the merging unit. The failures
are detected either by the negative sequence-based algorithm
or by the delta voltage and delta current algorithm. Upon
detecting a fault, the fuse failure supervision function activates
an alarm.
The trip-circuit supervision continuously monitors the
availability and operability of the trip circuit. It provides open
circuit monitoring both when the circuit breaker is in its closed
and in its open position. It also detects loss of circuit-breaker
control voltage.
8. Access control
To protect the merging unit from unauthorized access and to
maintain information integrity, the merging unit is provided with
a four-level, role based authentication system with
administrator-programmable individual passwords for the
viewer, operator, engineer and administrator levels. The access
control applies to the Web HMI and PCM600.
9. Inputs and outputs
Depending on the analog input option selected, the merging
unit is equipped either with three phase-current inputs, one
residual-current input and three phase-voltage inputs or
alternatively with one conventional residual current (Io 0.2/1 A)
input and three sensor inputs for the direct connection of three
combi sensors with RJ-45 connectors. As an alternative to the
combi sensors, separate current and voltage sensors can be
used utilizing adapters.
The phase current inputs are rated 1/5 A and the residual
current input is 0.2/1 A. The three phase voltage inputs cover
the rated voltages 60...210 V. Both phase-to-phase voltages
and phase-to-earth voltages can be connected. However,
phase-to-earth is recommended as the residual voltage can
only be derived from the phase-to-earth voltages.
Enhanced with optional hardware and software, the merging
unit also features three light detection channels for arc fault
detection in the circuit breaker, busbar and cable compartment
of metal enclosed indoor switchgear. The arc fault detection
sensor interface is available on the optional communication
module. The tripping decision is made by another protection
device also typically combining several different criteria like
checking of the fault current level.
Depending on the selected application configuration, the
merging unit includes either 4 PO + 2 SO (a total of 6 binary
outputs) or, when selected with the physical interface into the
switchgear primary equipment, 8 binary inputs and 4 PO + 2 SO
+ 3 HSO (a total of 9 binary outputs). The high-speed binary
outputs (HSO) decrease the total operate time typically with
4...6 ms compared to the normal power outputs.
All binary input and output contacts are freely configurable with
the signal matrix or application configuration functionality of
PCM600.
Substation Merging Unit
1MRS758420 B
SMU615
Product version: 1.0
ABB
9
