Closing a generator breaker onto the grid might seem like a simple procedure, but a careless moment can shock the engine and cause serious damage. Couplings fracture. Breakers and alternators absorb the impact. The solution is simple: synchronization. This guide shows how to synchronize a generator with Woodward governors and ComAp controllers safely.
What Is Grid-Tie Synchronization?
A grid-tie generator is a prime mover that runs in parallel with the utility grid. Prior to connecting, the generator voltage, frequency, and phase angle must track the grid within set limits. In addition, the phase sequence of the generator must align with that of the grid. The phase sequence is a one-time check during installation, while the other three factors are continually variable. When the controller detects these values match, it closes the generator breaker to the grid.
Why Good Synchronization Matters
Poor synchronization can do far more than damage the generator. It can stress the entire power train, causing couplings to crack and bearings to wear. It can also negatively affect power quality, causing dips and nuisance trips at the connection point. For industrial facilities with critical loads, synchronization is a vital process for maximizing power availability and reliability. In addition, effective synchronization is often the most time-saving method of connecting a generator to the grid, ensuring it is always ready to support demand shedding, back-up generation, or exporting power.
Who Does What: The Roles of Each Device
Synchronization is a team effort among the controller, the governor, and the voltage regulator (AVR).
The Woodward Governor
The governor regulates the prime mover speed. This is a critical factor, since speed directly affects the frequency and phase angle of the generator voltage. The governor must respond predictably to speed change commands from the controller during synchronization. Depending on the application and engine type, a Woodward governor can have a range of interface options including mechanical-hydraulic, mechanical-electronic, and electronic with an electronic actuator. The particular Woodward speed control has a direct impact on the available commands and communication options when syncing with a ComAp controller.
The ComAp Controller
ComAp designs and manufactures a range of controller solutions for single set, parallel set, and grid-tie applications. The controller acts as the system brain, measuring the frequency, voltage, and phase of both the grid and the generator. It then uses this information to modify the prime mover speed and close the generator breaker at the correct moment to match the grid.
The type of actions performed by the controller depends on the particular product type. Most controllers offer a variety of protection, load control, alarm, and communication features. Always refer to the datasheet and manuals for your particular controller solution.
The Voltage Regulator (AVR)
The AVR regulates the voltage of the generator and is adjusted by the controller to maintain a set level relative to the grid voltage. This process is critical for stable synchronization and load sharing.
The Circuit Breaker
The circuit breaker connects the alternator to the grid. The controller needs to know the breaker’s closing time characteristic to time the breaker engagement slightly earlier so the contacts meet at the correct moment.
How the Controller and Governor Talk
The controller must send speed change commands to the governor. There are several methods of doing this, depending on the available interface options for both devices including:
- Analog speed bias: The controller applies a small analog signal to the governor’s synchronization input to adjust the speed reference
- Raise/lower contacts: The controller applies a contact closure to raise or lower the speed reference in steps
- Digital communication: Some controllers and governors are capable of using a CAN-based communication link to send speed change commands
The choice of communication option depends on the available inputs/outputs for the governor and controller. Most woodward governors accept a range of analog and contact input options. Check the technical specifications for your particular governor model, then match it to the available outputs for your ComAp controller. Follow the wiring diagrams in the manuals for the correct installation and configuration.
Step-by-Step: How Synchronization Works
The image below shows a simplified block diagram of the synchronization process. This shows the basic steps involved in grid-tie synchronization of a prime mover:
- Start-up and speed regulation
- Voltage generation
- Grid and generator frequency, voltage, and phase angle measurements
- Speed adjustment
- Voltage adjustment
- Phase angle comparison
- Closing the breaker when the voltage, frequency, and phase angle are within set limits
The controller continually compares these variables and looks for a period of stability, defined by the voltage, frequency, and phase angle limits. This minimizes the risk of a breaker closing on a coincidental match of these variables.
Before You Commission: Key Checks
Thorough preparation can help avoid many common synchronization issues.
Verify Phase Sequence
Check that the phase sequence is correct before attempting to synchronize. A mismatched phase sequence cannot be synchronized and can damage the generator and prime mover if the breaker is closed.
Check Measurement Wiring
The controller must measure the grid and generator voltage accurately to perform synchronization. Check the potential transformer and current transformer ratios, polarity, and wiring.
Prove the Governor in Island Mode
Test the governor’s ability to maintain speed regulation in island mode before attempting to synchronize. This confirms that the governor will not hunt under load following.
Confirm Linkage and Actuator Movement
Make sure that the linkage and actuator move freely throughout their range. Slack in the linkage and play in the actuator can affect the precision of speed control.
Check the Speed Bias Range
The range of the speed bias signal must be sufficient to allow the controller to match the grid frequency. If the range is too small, the controller will not be able to accelerate or decelerate the prime mover quickly enough. If the range is too large, the response will be inaccurate and hunting may occur.
Setting the Synchronization Windows
The controller must be able to recognize when the frequency, voltage, and phase angle of the generator match the grid. These tolerances are often referred to as windows or limits and should be set according to the requirements of the utility and equipment manufacturer. These settings typically include:
- Voltage window: The acceptable range of voltages for synchronization
- Frequency window: The acceptable range of frequencies for synchronization
- Phase angle window: The acceptable range of phase angles for synchronization
- Dwell time: The period of stability required before breaker closing
- Breaker closing time: The time between breaker closing signal and actual contact closure
Narrow windows provide a more stable connection but require more time to achieve synchronization. Wider windows allow faster synchronization but can result in a more abrupt connection. Always follow the recommendations of the utility and equipment manufacturer. Never loosen limits to allow synchronization.
Droop and Isochronous: What Happens After the Breaker Closes
The type of governor control mode in use will affect synchronization performance after the breaker closes.
Isochronous governors maintain a constant frequency, which is ideal where a single generator is in use. However, this does not allow for stable synchronization in parallel with a stiff grid. In this configuration, the grid sets the frequency and the two systems fight for control.
A droop characteristic allows the frequency to vary slightly with load, which is necessary for stable load sharing in parallel with other prime movers. Many grid-parallel systems use either a droop characteristic or a load-following control mode to allow stable synchronization.
The correct mode of operation will be determined by the system requirements. Always confirm the intended mode of operation with your system designer or manufacturer.
Load Control After Synchronization
Once the generator has been synchronized, the controller must manage the load. Some common load control methods include:
- Base load: The controller maintains a set power output
- Peak shaving: The controller increases power output when demand exceeds a set limit
- Import/export control: The controller maintains a set power level at the connection point
- Ramping: The controller gradually changes the power output to protect the engine
Stable load control requires a responsive governor. A sluggish governor will result in load hunting. Always optimize the governor and controller settings together.
Protection You Must Not Skip
- Grid-tie systems require protection for both the generator and the utility network.
- Reverse power protection prevents the generator from being driven as a motor
- Loss-of-mains protection disconnects the generator in the event of a grid failure
- Over and under voltage and frequency protection trips the generator in the event of abnormal conditions
- Synchro-check protection prevents breaker closing under abnormal conditions
Many utilities require protection relays and testing before connection. Always confirm requirements with the local utility and never attempt to connect a generator in parallel without authorization.
Common Synchronization Problems and Fixes
The table below shows some common synchronization problems and potential causes. Always refer to the relevant section in your controller documentation for more information.
| Problem | Likely Causes to Check |
|---|---|
| Generator Will Not Synchronize | Speed bias wiring, governor stability, incorrect synchronization window, or wrong phase sequence |
| Speed Hunts Near the Grid | Governor gain, mechanical linkage play, noisy signals, or incorrect droop settings |
| Breaker Closes with a Bump | Synchronization window too wide, slow breaker operation, or incorrect voltage matching |
| Load Swings After Closing | Load control tuning, governor response, or fuel system issues |
| Reverse Power Trip | Poor load pickup, incorrect protection settings, or fuel/governor faults |
| Trips on Grid Failure | Loss-of-mains settings, incorrect measurement points, or utility interconnection requirements |
A Simple Real-World Example
The example below describes a typical application for grid-tie synchronization. A manufacturing facility wishes to operate a standby generator in parallel with the grid to reduce peak demand. The team performs a proof test of the governor in island mode before proceeding to commission the generator in parallel with the grid.
- Mechanical inspection: The team inspects the linkage and checks the actuator travel. They confirm there is no slack in the linkage and the actuator moves freely throughout its range.
- Electrical inspection: The team checks the connection between the ComAp controller and the governor. They confirm that the controller outputs the correct speed bias signal range and that the signal is not noisy.
- Governor in island mode: The team tests the governor in island mode and confirms that it maintains a stable speed under varying loads.
- Set up the controller: The team sets up the controller for synchronization using the settings in the manual. They confirm that the speed bias range is correct and that the windows for frequency, voltage, and phase angle are set appropriately.
- Test synchronization: The first parallel test begins and the controller matches the frequency and voltage of the grid. It then waits for the phase angle to be within the set window before closing the breaker to the grid. The team observes the results and notes all settings made to the controller.
Maintenance Habits That Keep Synchronization Reliable
As mentioned previously, synchronization problems often develop gradually. Routine maintenance can identify and resolve many issues before they cause downtime or damage.
- Linkage inspection: Always inspect the linkage and actuator for tightness and free movement at every service
- Terminal and grounding check: Check that all terminals are tightened and shields are grounded correctly
- Speed sensor signal and gap check: Routine tests of the signal and gap are essential for maintaining synchronization performance
- Alarm history and event logs: These features can provide valuable insight into synchronization problems
- Breaker closing time and operation test: Always test the breaker operation and closing time as per the maintenance schedule
- Protection relay testing: Test all protection relays in accordance with the requirements of the utility and equipment manufacturer
It is good practice to perform a routine test synchronization during any generator downtime, rather than waiting to identify a problem.
Common Installation Mistakes
- Skip the phase sequence check
- Ignoring governor stability issues
- Using the wrong speed bias range
- Widening sync windows to hide a fault
- Forgetting the breaker closing time
- Running signal wires alongside power cables
- Making multiple changes at the same time
When making adjustments, always make one change at a time and document any modifications.
- Tips for Buying Governors and Controller Parts
- Always purchase identical models for each component
- Confirm that the governor and controller are compatible with the same signal type
- Ask whether the part is original, new, or remanufactured
- Request documentation and warranty information
- Keep spares for actuators, speed sensors, and critical controller accessories
- Choose a supplier who can answer technical questions
Safety First
Synchronization work always involves high voltages and powerful machines.
- Always lock out and tag out circuits before testing or maintenance work
- Assume all circuits are live until proven otherwise
- Never bypass the synchro-check function
- Only qualified technicians should commission grid-parallel systems
- Coordinate with the utility before first parallel operation
Frequently Asked Questions
Why must a generator match the grid before closing?
Failure to match the grid can cause large current and mechanical shocks that damage the engine, alternator, coupling, and breaker.
Can I use any Woodward governor with a ComAp controller?
While a range of Woodward governors can be used with ComAp controllers, the controller must be able to send the correct speed command to the selected governor.
What causes a generator to hunt while synchronizing?
Unstable governor tuning, linkage play, noisy signals, and incorrect speed bias range are common causes of hunting.
Do I need utility approval for grid-parallel operation?
In most cases, yes. Many utilities require specific protection and testing before allowing a grid-parallel connection.
Where can I buy reliable Woodward governors?
Always deal with a supplier who can confirm part numbers and provide technical support. Jawaid Enterprises can help match you with the right Woodward governors for your system.
Conclusion
Achieving smooth grid connection requires a stable governor, accurate measurements, and appropriate controller settings and protection. By following the correct procedures and performing regular maintenance, you can minimize the risk of synchronization problems.
Make sure to check the phase sequence and perform a proof test of the governor in island mode. Set the windows appropriately and ensure the controller is using the correct speed bias range. Always make one change at a time and test the controller settings. These practices will significantly reduce the risk of synchronization faults.
The correct choice of Woodward governors and controller parts makes all the difference. If you are looking for governors, actuators, or advice on selecting the right solution, contact Jawaid Enterprises today. We can help you choose the best combination of parts for your engine and controller type.
Need woodward governors? Contact Jawaid Enterprises at jawaidenterprises.com today.