ACB Trouble. The generator does not connect to the main busbars. Troubleshooting

Greetings! In this article will discuss one of the problems with diesel generators, which is possible and rare, but happens on ships. In general, any problem with generators for an ETO is a sore and most discussed topic.

Also here we will briefly examine the conditions for synchronizing ship synchronous generators (alternators).

So, let's go! When we try to connect the first diesel generator to the main busbars, the ACB Trouble error (ACB NONC - ACB no close) appears, it does not connect to the busbars, the diesel continues to run at idle.

TAIYO GE41B-8 600kVA Brushless Synchronous Alternator

At the same time, the third diesel generator is connected to the main busbars and supplies the ship’s power station with electricity. After the alarm is reset, the attempt is repeated and fails again.

Alarms in AMS BEMAC BE-D10

We're starting to figure out what's going on. On full automatic vessels, engineers have long become lazy (in the good sense of the word), they have forgotten about the synchronization conditions and no longer remember what devices should be in sight when the generator is taken to the busbars. Automation does everything for the operator and therefore, over time, natural relaxation occurs. As you understand, it was a joke and everything, of course, depends on the human factor.

ACB Trouble reset

That is why attempts are repeated, although the root cause lies on the surface. Now is the time - you pressed the button and left to do other work, the automation will work for you.

We will analyze the conditions for synchronizing ship synchronous alternators, without exact numbers.

Synchronization conditions for alternators:

1. The frequency on the buses and the connected generator must match.
2. The voltage on the busbars and the EMF (electromotive force) of the connected generator must match.
3. The shift angles (phase angles) between the bus voltage and the EMF of the connected generator must match.

There is one more condition - this is the coincidence of the order of phase alternation. This condition is ensured during the initial installation of the generators and the ship's power plant, so it is satisfied.

The Electromotive Force (EMF) of a generator refers to the voltage generated by the machine. This voltage is induced by the relative motion between a magnetic field and a conductor. The fundamental principle behind the generation of EMF is Faraday's Law of Electromagnetic Induction, which states that a change in magnetic flux through a circuit induces an EMF in the circuit.

The EMF $E$ generated by a generator can be expressed by the formula:

$E = N \cdot \frac{d\Phi}{dt}$

where:

• $N$ is the number of turns in the coil,
• $\Phi$ is the magnetic flux through a single loop of the coil,
• $\frac{d\Phi}{dt}$ represents the rate of change of magnetic flux.

In a rotating generator, the EMF can also be described by the equation:

$E = N \cdot B \cdot l \cdot v$

where:

• $B$ is the magnetic flux density,
• $l$ is the length of the conductor within the magnetic field,
• $v$ is the velocity of the conductor relative to the magnetic field.

For an alternating current (AC) generator, the EMF varies sinusoidally over time and is given by:

$E(t) = E_{\text{max}} \cdot \sin(\omega t)$

where:

• $E(t)$ is the instantaneous EMF,
• $E_{\text{max}}$ is the maximum value of the EMF,
• $\omega$ is the angular frequency of rotation,
• $t$ is time.

This variation in EMF is what leads to the generation of AC power in generators.

The operator is interested in the first three conditions. Usually, the first two conditions are checked while the diesel engine is idling, i.e. coincidence of frequencies and voltages.

Bus frequency and generator frequency

The photo above is just an example. Usually there are two frequency meters that show the frequency on the buses and the frequency of the connected generator. There are also dual frequency meters on ships.

EMF of the connected generator

The EMF of the connected generator and the voltage on the buses are monitored using separate voltmeters. There are also dual voltmeters on ships.

Example of a dual frequency meter and voltmeter

The execution of the third condition is ensured by the synchronoscope, i.e. the generator must be connected on the busbars, taking into account the equality of the shift angles between its EMF and the voltage on the busbars.

In practice, you need to connect it according to the synchroscope needle at the 12 o'clock position, taking into account the delay in operation of the circuit breaker of 5 seconds, you must give the command without 5 seconds 12. It is very important that the hand rotates slowly clockwise, otherwise you can connect the generator to the main busbars in motor mode, although the protection it simply won't let you do it.

Synchronoscope. The generator is connected to the main busbars

Today, most modern ships have automatic synchronization systems that perform all of the above actions for the engineer. Each vessel always has a manual mode, which many people are slowly starting to forget about :)

In the operator's line of sight, when taking the generator in parallel, there should be instruments: a synchroscope, a dual voltmeter and a frequency meter.

Let's return to our problem. If you pay attention to the frequency meter, which shows the generator frequency is more than 61 Hz, while the frequency on the buses is about 60 Hz, then the situation begins to become clearer. One of the synchronization conditions is not met, namely, the frequency of the connected generator is not equal to the frequency on the buses.

Bus frequency

Generator frequency

In the photos above the frequencies on the buses and the connected generator are equal.

Unfortunately, I didn’t take a photo of the frequency discrepancy.

In this case, usually the PMS (Power Management System) automation should adjust these parameters by influencing the speed controller (Governor), but in this situation the automation does not do this, generates an error and stops the process of connecting to the main busbars.

A Power Management System (PMS) for generators on a vessel is a critical component designed to ensure the efficient and reliable operation of the ship's electrical power network. Here are its key functions and features:

1. Load Management:

   • Automatic Load Sharing: Distributes the load evenly among generators to prevent overloading and optimize fuel efficiency.
   • Load Shedding: Disconnects non-essential loads during high demand or generator failure to maintain power to critical systems.

2. Generator Control:

   • Start/Stop Control: Automates the starting and stopping of generators based on the power demand and operational conditions.
   • Synchronization: Ensures generators are synchronized in terms of voltage, frequency, and phase before connecting to the busbar.

3. Fault Detection and Protection:

   • Fault Isolation: Detects and isolates faults to prevent damage and ensure safety.
   • Alarm Systems: Provides alerts for abnormal conditions such as overvoltage, undervoltage, overcurrent, and short circuits.

4. Redundancy and Reliability:

   • Redundant Systems: Ensures continuous power supply by having backup generators and redundant control systems.
   • Automatic Transfer: Transfers load to standby generators in case of primary generator failure.

5. Monitoring and Reporting:

   • Real-time Monitoring: Monitors the status of generators and power distribution in real-time.
   • Data Logging and Reporting: Logs operational data for maintenance, analysis, and regulatory compliance.

6. User Interface:

   • Control Panels: Provides user-friendly interfaces for manual control and monitoring.
   • Remote Monitoring: Enables remote access to the PMS for oversight and diagnostics.

The PMS is essential for ensuring the vessel's power system's efficiency, safety, and reliability, thereby supporting the vessel's operational requirements and minimizing the risk of power-related issues.

PMS BEMAC UGS-21

This time I was lucky enough to work on a Japanese BEMAC, although recently I have come across the Danish DEIF system more and more often.

PMS DEIF

The implementation of the third condition of synchronization using an LED synchroscope is very clearly implemented on the BEMAC. You can watch a video of the synchroscope at the end of this article.

The next step was to find out if the problem was with the PMS or the speed controller. To do this, the system was switched to manual mode in order to manually operate the diesel speed controller using the Lower - Raise handles (in simple terms, Less / More).

Operating mode switch (Manual / Automatic)

Handle (Less / More)

As a result of an attempt to influence the speed (fuel rail) and, accordingly, the frequency using the handle, it turned out that the speed controller does not work in manual mode. That is, the regulator cannot adjust the generator frequency to the frequency on the buses, either in automatic or manual modes.

The next action is to find out whether the command is coming from the handle, and accordingly from the PMS to the regulator motor. To do this, you need to measure the incoming voltage to the servo motor when the corresponding command is given.

Scheme of operation of the governor motor

In my case, the governor on the Japanese YANMAR 6EY18AL engine is installed, respectively, with a hydraulic YANMAR NZ61 with a single-phase reversible AC 220V motor.

Hydraulic governor YANMAR NZ61

To do this as accurately as possible, it is advisable to take measurements directly at the motor terminal box (bypassing all the cables and connections in the junction boxes). In this case, we are lucky that we can open the top cover of the governor and immediately get access to the motor terminal block.

Motor terminal block

Governor transmission mechanism diagram

During the initial inspection, it was discovered that in order to check the free rotation of the motor it is necessary to disconnect it from the friction clutch and move it away from the governor body.

Motor operation diagram

Motor operation diagram (in our example without limits). Capacitor parameters

According to the motor operation diagram, all connections were checked, as well as the capacitor. It turns out that the connections on the capacitor are in poor condition and should be replaced. Pulling the cable, it simply came off the terminal block. A similar problem was described in the article about the main engine.

Poor connection on the capacitor

Checking the capacitor (ok)

Capacitor checked and connections updated. Next, the incoming voltage to the terminal block was checked, according to the diagram. It turned out that the voltage is 220 V, but there is no rotation of the motor (in both directions).

Checking the motor

The next step was to check the free rotation of the motor. The electric motor rotates by hand, but as a result of applying power to it, it jams in one position. It turned out that the motor had an interturn short circuit.

Troubleshooting from the manufacturer

It is interesting that Troubleshooting from the maker does not describe the problem with the electric motor at all.

Disassembling the motor

When disassembling the motor, it turned out that the silicone bearing sleeve had crumbled, and apparently the rotor, which was rubbing against the stator, was displaced, which led to an interturn short circuit.

Installation of the working motor

As a result, a working motor was installed. Due to the lengthy efforts to fix the problem, we first had to manually adjust the frequency, because it went below 55 Hz.

Frequency below 55 Hz

Frequency adjustment video

After adjusting the frequency, the system was switched to automatic mode and the generator was successfully paralleled.

Air circuit breaker is connected

The ACB Trouble error (ACB NONC - ACB no close), which was written about at the beginning of the article, in this situation can lead to confusion when searching for the problem. Because translated as Air circuit breaker no close, i.e. there is a problem with the generator circuit breaker (does not connect to the main busbars). It turns out that this is a general alarm, and in this case it does not relate to the circuit breaker, it signals the impossibility of connecting the generator to the main busbars, and this could be anything. There is no more information and you have to return to the synchronization conditions and check each parameter separately.

Video of the YANMAR NZ61 governor in operation

Full video of connecting the second generator to the main busbars

Once again, let’s return to the synchronization conditions and steps for manual synchronization.

Synchronization conditions for alternators

Synchronization of alternators, also known as synchronizing or paralleling, is the process of matching one alternator (generator) with another alternator or with the grid. This is critical for ensuring smooth and stable operation of multiple generators or for connecting a generator to the grid. There are several conditions that must be met for successful synchronization:

1. Voltage Matching

The voltage of the incoming alternator must match the voltage of the system or grid to which it is being synchronized. This ensures that there is no large voltage difference that could cause a surge or fault.

2. Frequency Matching

The frequency of the incoming alternator must be the same as the frequency of the system or grid. This is crucial to prevent phase differences that could cause power oscillations or damage to equipment.

3. Phase Sequence Matching

The phase sequence of the incoming alternator must match the phase sequence of the system or grid. This ensures that the phases are aligned correctly and prevents issues such as reverse power flow.

4. Phase Angle Matching

The phase angle of the incoming alternator must be closely aligned with the phase angle of the system or grid. Ideally, the phase angle difference should be very small (close to zero) at the moment of synchronization to minimize transient currents.

Methods for Synchronization

There are several methods used to achieve these conditions:

1. Three Lamp Method

Three lamps are connected between the corresponding phases of the incoming alternator and the busbar. When the alternator is synchronized, all three lamps will dim and brighten together, indicating matching frequency and phase. The lamps will be dark at the instant of perfect synchronization.

2. Synchroscope

A synchroscope is an instrument that shows the phase angle difference and whether the incoming machine is running faster or slower than the busbar. The pointer on the synchroscope will move toward the '0' position when the conditions for synchronization are met.

3. Automatic Synchronization

Automatic synchronizers use sensors and control systems to automatically adjust the alternator's voltage, frequency, and phase angle to match the system or grid. Once the conditions are met, the synchronizer closes the circuit breaker to connect the alternator to the system.

Steps for Manual Synchronization

1. Adjust the Voltage: Use the voltage regulator to match the alternator's voltage with the busbar voltage.
2. Match the Frequency: Adjust the speed of the prime mover to match the alternator frequency with the busbar frequency.
3. Check Phase Sequence: Ensure the phase sequence of the alternator matches the busbar.
4. Align Phase Angles: Use the synchroscope or three lamp method to align the phase angles.
5. Close the Circuit Breaker: Once all conditions are met, close the circuit breaker to connect the alternator to the system.

Meeting these conditions is essential to ensure that the alternators or generator and grid operate in harmony, avoiding potential damage and ensuring a stable power supply.