Stopping, trips and AMS alarms

CHIEF. LEARN · Guide 4 of 5

Stopping a main air compressor, emergency stop, trips on low oil pressure, high temperature and overload, reset, and the RUNNING, HEALTHY, FAIL TO START signals.

The example throughout is No.1 main air compressor of a ship: a 30 kW motor on a 440 V, 60 Hz supply with a relay starter panel (SP-MAC1) and 220 V control voltage, charging two 3 m³ receivers to 30 bar.

NC / NO: normally closed / normally open contact
AMS: alarm and monitoring system
ECR: engine control room
HMI: human–machine interface: the display on the panel door

Stopping

Running in MAN

Mechanics: Loaded, pumping.
Electrics: Wire 26 live: H2, K10, P2, KT3, YV3; wire 29 live: YV1 and YV2 closed.
What you see and hear: RUNNING, about 46 A.

STOP

Mechanics: The motor coasts down. YV1 and YV2 open, blow out the condensate and unload both stages. They stay open while it stands.
Electrics: KM1 drops: wire 26 dead, so YV1/YV2 lose their supply (open), YV3 closes the water, RUNNING goes out, the running-hours meter stops. KM1 21-22 closes: the motor heater is on. KT1 and KT3 reset.
What you see and hear: A blast from both drains, then quiet.

Emergency stop

Mechanics: KM1 drops out at once; the compressor runs down.
Electrics: S0 at the compressor is the first contact of the protection chain: everything after wire 3 is dead. K11 drops: the AMS shows MAC1 SHUTDOWN. It cannot be restarted while S0 is latched.
What you see and hear: POWER ON stays lit (it is before S0), RUNNING out, HMI EMERGENCY STOP.

Releasing the emergency stop

Mechanics: Ready to start again.
Electrics: Wire 3 to wire 6 live again, K11 HEALTHY back. In MAN it needs START; in AUTO it starts by itself if there is demand. This design does not latch the emergency stop; many makers do, so that a reset is needed before any restart (IEC 60204-1).
What you see and hear: HMI alarm returns to normal.

Protections and reset

Low oil pressure

Mechanics: The pump makes only 0.5 bar here. After the 20 s bypass the compressor trips.
Electrics: KT1 15-18 closes with PS3 still closed: KA2 pulls in, latches through S5 (NC) and its own 21-24, and opens the chain with 11-12. KA2 31-34 lights TRIP.
What you see and hear: TRIP lit, HMI LO PRESS LOW SHUTDOWN.

Reset

Mechanics: Find the cause first. Here the oil pump has been put right.
Electrics: RESET S5 is NC: pressing it breaks the latch of KA2 and KA3. Then start again.
What you see and hear: TRIP out.

High temperature

Mechanics: No cooling water: water out and delivery air heat up.
Electrics: TS1 (air above 80 °C) or TS2 (water out above 60 °C) closes onto wire 24: KA3 pulls in and latches like KA2.
What you see and hear: Without water the delivery air heats up faster than the water: HMI AIR TEMP HIGH at 75 °C, then AIR TEMP HIGH SHUTDOWN.

Overload

Mechanics: Running at 30 bar with F4 set to 40 A instead of 50 A.
Electrics: 47 A is normal, but above the wrong setting: the bimetals heat up until F4 opens 95-96 and closes 97-98 (TRIP). It resets by hand with the blue button once the bimetals have cooled.
What you see and hear: TRIP lit, the red flag on F4. Set Ir back to 50 A.

Signals to the AMS

Three dry contacts

Mechanics: Stopped.
Electrics: K10 RUNNING on wire 26 (X3:1-2), K11 HEALTHY on wire 6 (X3:3-4), K12 AUTO DEMAND on wire 31 (X3:5-6). HEALTHY is fail-safe: closed means power present and no trip; open gives MAC1 SHUTDOWN / CONTROL POWER FAIL.
What you see and hear: Only K11 is on.

Running in AUTO

Mechanics: Started on demand.
Electrics: K12 (demand) and K10 (running) both closed.
What you see and hear: All three interface relay LEDs lit.

FAIL TO START

Mechanics: Demand, but the contactor cannot pull in (open coil).
Electrics: The AMS sees K12 closed and K10 open for more than 10 s: MAC1 FAIL TO START. That is how an open contactor coil reaches the ECR and the duty engineer.
What you see and hear: AMS alarm MAC1 FAIL TO START.

For training only. Models are simplified; class rules and the maker’s manual are the authority.