Introduction
The system is a three-phase Uninterruptible Power Supply (UPS). The system uses a flywheel to store energy mechanically in the form of a rotating mass. During normal operation, the flywheel will be rotating at a constant speed. The typical speed of the flywheel is 7700 RPM. The power from a utility will be delivered by the system to an external load. When power from the utility is interrupted, the system will convert the mechanical energy that is stored in the flywheel to electrical energy. This energy will be used by the external load. When the power from the utility is available again, the system will transfer the load back to the power from the utility.
Diagram of the System
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| Illustration 1 | g01089571 |
Illustration 1 shows a simplified diagram of the system. The nodes that are shown in illustration 1 are in the following list: Input, Filter and Output.
The nodes determine the state of the system. The input node and the output node are externally available. These nodes are used in order to attach the system to a power source and to the load. The filter node is used internally by the system.
The DC Bus is also identified in illustration 1. The DC Bus is used as a power source for the field coil currents. The mode of the system determines if the bus is used as a power source for the flywheel or as a power source for the utility inverters.
The main functional blocks are shown in illustration 1. A description of each function is in the following list:
Input Contactor - A mechanical contactor that is used to control the flow of electricity into the system
Output Contactor - A mechanical contactor that is used to control the flow of electricity to the load
Static Switch - The switch is a semiconductor device (thyristor). The Static Switch is used to isolate the system from the utility grid when an outage occurs.
Utility Inverter - The Utility Inverter is a semiconductor device that is used in order to rectify the AC voltage that is on the filter node into a DC voltage. When the power from the utility is lost, the utility inverter will convert the voltage from the DC Bus to the operating voltage and frequency of the system.
Flywheel Inverter - The Flywheel Inverter is a semiconductor device that is used to convert the voltage from the DC Bus into AC signals. When the power from the utility is not available, the flywheel inverter will rectify AC signals from the flywheel to the DC Bus.
Field Coil Driver - The Field Coil Driver is a semiconductor device that is used to drive current through the field coils. The field coils are used to generate magnetic forces that act upon the flywheel. These forces are controlled in order to provide a lifting force on the flywheel. The force prolongs the life of the bearings.
Control Signals and Telemetry Signals Prior to Version 2.4
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| Illustration 2 | g00984430 |
The Control signals that are sent from the system controller | |
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| Illustration 3 | g00802130 |
The Control signals that are sent to the system controller | |
Control Signals and Telemetry Signals for 2.4 Release
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| Illustration 4 | g01049001 |
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| Illustration 5 | g01049046 |
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| Illustration 6 | g01049049 |
Modes of Operation
The UPS functions automatically in order to supply AC electrical power to the critical load. There are several operation modes that allow the UPS to accomplish this task. Most of the operating modes have several states that occur in that mode. The mode and the state are displayed on the LCD display. The LCD display is located on the front panel. The operating modes are listed below:
- On-line Modes
- Bypass Modes
- Automatic Voltage Regulation Mode
- Manual Mode
- Calibration Mode
The UPS continually monitors internal systems and the incoming utility power. The UPS automatically toggles between the modes that are listed above, and without intervention by an operator. The detection logic and the switching logic that is programmed into the UPS ensures that operating mode changes are automatic and transparent to the critical load.
On-line Modes
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| Illustration 7 | g01089448 |
On-line
On-line mode is the standard operating mode for the system. When the system is in this mode, the load is protected. The system is capable of discharging in order to support the load.
On-line Charging
The system enters this state when the flywheel reaches 4000 RPM. The system is charging in this state. The system can sustain discharge in this state.
On-line Standby
When the speed of the flywheel reaches 7700 RPM, the system is in the On-line standby state. This is rated idle speed for the flywheel.
On-line Discharging
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| Illustration 8 | g01089519 |
The system is in this state when the unit is supplying power to the load. If there is a disruption in power, the system will change to this state.
On-line Self-Discharge
This state stops the flywheel electrically. This state is used for the following:
- Prepare the system to be moved.
- Secure the system for maintenance.
- The On-line Self Discharge Mode can be entered once in a 24 hour time period.
Bypass Modes
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| Illustration 9 | g01089543 |
The bypass circuit powers the critical bus for one of the following reasons:
- Maintenance is required.
- The UPS can not maintain voltage to the load due to an overload that was sustained or a malfunction that occurred.
The bypass circuit also provides a path for power from an alternate AC source. The control system of the UPS constantly monitors the availability of the system bypass circuit in order to perform a transfer. The system bypass circuit consists of the following components:
- Static bypass switch
- Output contactor
- Circuit Breaker (System Bypass)
Note: The Static Bypass Switch is an option.
The output contactor isolates the module outputs of the UPS. The Circuit Breaker (System Bypass) works in parallel with the optional static bypass switch. The static bypass switch is a solid-state device that can connect the alternate AC source to the load instantly.
Bypass
Bypass mode directly connects the incoming utility to the system load. When the system is in the bypass mode, the load is not protected. The load can be affected by a disruption of incoming power. The Bypass mode is entered by one of the following events:
- Start-up
- The Keyswitch (Manual)
- Failure to Recover From a Fault
Repeated errors that cause the system to oscillate between the bypass mode and On-line mode can lock the system into the bypass mode. When the system is locked in the bypass mode, the user must change the mode of the system. Use the keyswitch in order to change the mode of the system.
"Bypassed-Verify" Signals - When the system is in this state, the system verifies that the correct system telemetry is present. This state is used when you are starting the system and the state is used during the recovery of errors.
"Bypassed-Auto Start" - This is the default state at start-up. The system cannot immediately protect the load after the system is started. During the normal operation, the system will enter Automatic Voltage Regulation mode.
Automatic Voltage Regulation Mode
The Automatic Voltage Regulation Mode can be entered by one of the following events:
- Start-up
- Error (Flywheel)
Automatic Voltage Regulation Auto Start State
The system remains in the Automatic Voltage Regulation Mode until the system is charged and until the system is able to sustain discharge. During the Automatic Voltage Regulation Auto Start State, the flywheel must achieve a rate of 45 RPM before changing to the Automatic Voltage Regulation Charging state.
Automatic Voltage Regulation Charging
The system enters this state when the system starts to charge the flywheel. When the speed of the flywheel is greater than 7700 RPM, the system enters the On-line Standby state. Normally, the system enters the On-line Charging state when the flywheel reaches 4000 RPM.
Automatic Voltage Regulation Verify Signals
When the system is in this state, the system verifies that the correct system telemetry is present. This state is used when you are starting the system and the state is used during the recovery of flywheels errors.
Manual Mode
The manual mode is intended to be used by service technicians. When the system is in the manual mode, a technician can conduct diagnostic tests of the subsystems. This mode is only accessible to qualified service personnel.
Calibration Mode
Calibration Mode is used in the factory during the initial calibration.
"Calibration - Calibration Point" - The system uses this state to calibrate a telemetry channel.
Calibration-Energizing - This state is used during sensor calibration. This state energizes the flywheel. The flywheel spins to several hundred RPM.
Calibration-Auto Adjusting - This state adjusts the commutation of the flywheel in order to maximize charging.
Redundant (N+1) Option
A redundant (N+1) system is sized with an additional Multiple Module Unit. In this configuration, the loss of one MMU will not cause the system to drop the critical load. The malfunction of one of the Multiple Module Units will cause the Multiple Module Unit with the fault to be disconnected from the critical load. The remaining Multiple Module Units will continue to carry the load. After the Multiple Module Unit has been repaired, the unit can be reconnected to the critical load. The System can then resume redundant operation.
If more than one Multiple Module Unit is removed from the system and if the load exceeds the capacity of the Multiple Module Units that are remaining on-line, there will be an automatic transfer of the load to the bypass line without an interruption of the power. Any redundant Multiple Module Units can be taken off the critical load manually for maintenance without disturbing the critical load bus. In this case, the isolation switches are used.
Systems without a Redundant MMU
In a system without a redundant MMU, all the Multiple Module Units will supply the full rated load. If the Multiple Module Units malfunction, there will be a transfer of the load to the bypass line without an interruption of power. Any Multiple Module Units can be taken off the critical load manually for maintenance without disturbing the critical load bus.
Load Sharing
In parallel operation, all of the inverter units automatically share the load at all times. The output current of individual Multiple Module Units will be no more than 15% unbalanced. The parallel load sharing function is programmed within each MMU. In (N+1) systems, the redundant MMU only shares the reactive current.
Manual Load Transfers
A manual load transfer between the output of the UPS and the alternate bypass AC source can be initiated from the control panel of the System Cabinet. Manually initiated transfers will make the connection to the alternate bypass AC source before breaking the connection. These transfers utilize the output of the UPS and the bypass circuit breakers (system).
Automatic Load Transfers
An automatic load transfer between the outputs of the inverter and the alternate bypass AC source is initiated if an overload condition is sustained for a time period in excess of the capability of the system output. An automatic transfer of the load may also be initiated due to a malfunction that would affect the output voltage. Transfers that are caused by overloads initiate an automatic transfer of the load back to the system again only after the load has returned to a level within the rating of the UPS. The internal programming of the UPS allows a transfer of the load back to the UPS up to three times. The transfers of the UPS back to the system are adjustable within ten minute periods in order to prevent cyclical transfers which are caused by overloads. On the fourth transfer, the system will lock into the bypass mode.
Momentary Overloads
The static bypass switch will connect the bypass AC source to the load and the static bypass switch will close the bypass circuit breaker (system) in one of the following cases:
- inrush of Load current
- The fault (branch load circuit) is in excess of the rating of the system. The transfer of the load to bypass mode will be uninterrupted.
Selective Tripping
Each MMU has a self-diagnostic capability. When a fault occurs in a Multiple Module Unit, the Multiple Module Unit that has a fault will identify the failure. This Multiple Module Unit will be subsequently removed from the critical bus. Selective tripping does not rely on information that is shared among Multiple Module Units.
Communication Between Multiple Module Units
Communication between the Multiple Module Units is provided by the System I/O Board via Category 5, 4 pair UTP-24 AWG shielded wire.
External Communications for the UPS
One of the Multiple Module Units in the system serves as the processor for the external communications. The system cabinet has a Parallel Cabinet Interface Board with a rotary switch that allows you to select the MMU that will be used for external communications. External communications can be done via one of the following methods: RS-232/RS-485 port, ethernet and modem.
Protection and Backfeed Prevention
The critical output bus is protected from the flow of excess current fuses. Each phase of the bypass circuit is protected by the bypass circuit breakers. Monitors for blown fuses indicate when a blown fuse will prevent the path for the static bypass switch from being available for automatic transfers.
The static switch (bypass) will not feed the power back from the UPS to the distribution system (bypass) while the UPS is operating on flywheel mode during a outage of the source voltage for bypass. The static switch (bypass) is provided with redundant circuits that sense outages in the bypass power. The system for backfeed prevention operates even if two component failures exist simultaneously. If a shorted SCR is detected, the static bypass switch is isolated. An alarm message will be annunciated at the control panel on the System Cabinet. The load shall remain on conditioned power and protected power after the detection of a shorted SCR and after the isolation of the static bypass switch.