Product Details
Speed Control and Overspeed Protection
Speed control and overspeed protection is implemented with six passive, magnetic speed pickups. The first three are monitored by the controllers, which use the median signal for speed control and primary overspeed protection. The second three are separately connected to the R8, S8, and T8 IS215VPROs in the protection module. Provision is made for nine passive magnetic speed pickups or active pulse rate transducers (TTL type)
on the TPROH1B terminal board with three being monitored by each of the R8, S8, and T8 IS215VPROs. Separate overspeed trip settings are programmed into the application software for the primary and emergency overspeed trip limits, and a second emergency overspeed trip limit must be programmed into the I/O configurator to confirm the EOS trip point.
The speed is calculated by counting passing teeth on the wheel and measuring the time involved. Another protection feature is: after the turbine reaches a predetermined steady-state speed, the rate of change of speed is continuously calculated and compared with 100%/sec and transmitted to the controller to trip the unit if it is detected. This steady-state speed limit is a tuning constant located in the controller’s application software. Another speed threshold which is monitored by the EOS system, is 10% speed.This is transmitted to the controller to verify that there is no gross disagreement between the first set of three speed pickups being monitored by the controller (for speed control and the primary overspeed protection) and the second set of three speed pickups being monitored by the EOS system.
Speed Difference Detection
There should never be a reason why the speed calculated by IS215VPRO is significantly different from the speed calculated by the main control. Speed difference detection looks at the difference in magnitude between pulse rate 1 from both IS215VPRO and the main control. If the difference is greater than the set threshold for three successive samples, a SpeedDifTrip is latched. If the main control recovers for 60 seconds, the trip is removed. This allows the main control to recover with subsequent re-arming of the backup protection.
Interface to Trip Solenoids
The trip system combines the Primary Trip Interface from the controller with the EOS Trip Interface from the protection module. Three separate, triple redundant trip solenoids (also called Electrical Trip Devices [ETD]) are used to interface with the hydraulics. The ETDs are connected between the TRPG and TREG terminal boards. A separately fused 125 V dc feeder is provided from the turbine control for each solenoid, which is energized in the run mode and de-energized in the trip mode.
Backup Synch Check Protection
Backup synch check protection is provided in the Protection Module. The generator and bus voltages are supplied from two, single phase, potential transformers (PTs) secondary output supplying a nominal 115 V rms. The maximum cable length between the PTs and the turbine control is 100 meters of 18 AWG twisted, shielded wire. Each PT is magnetically isolated with a 1,500 V rms rated barrier and a circuit load less than 3 VA.
The synch algorithms are based on phase lock loop techniques. Phase error between the generator and bus voltages is less than ± 1 degree at nominal voltage and 50/60 Hz. A frequency range of 45 to 66 Hz is supported with the measured frequency within 0.05% of the input frequency. The algorithm is illustrated under TTUR, generator synchronizing.
Each PT input is internally connected in parallel to the R8, S8, and T8 IS215VPROs. The triple redundant phase slip windows result in a voted logical output on the TREG terminal board, which drives the K25A relay. This relay’s contacts are connected in series with the synch permissive relay (K25P) and the auto synch relay (K25) to insure that no false command is issued to close the generator breaker. Similarly, contacts from the K25A contact are connected in series with the contacts from remote, manual synchronizing equipment to insure no false commands.
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