Type VRLTC load tap changer

Transcription

1 Pilot inspection report Type VRLTC load tap changer Product: Type VRLTC, on-tank, vacuum reactance load tap changer Rating: 1500 A, 150 kv BIL By: Jon Brasher - Technical Specialist and Senior Account Executive Bill Teising - Senior Development Engineer Type of unit VRLTC Full description Vacuum reactance, servo motor drive, TLMS monitoring system Data acquisition Compact RIO enabled online monitoring Unit model Unit current rating 1500A Unit BIL 150 kv Unit serial number L Application Retrofit Reason to replace Existing LTC at end of life Transformer make Federal Pacific Transformer year of manufacture 1976 Replaced LTC make Federal Pacific Replaced LTC model FP TC-25 Replaced LTC type Reactance, arcing under oil Date of installation 21-Jan-12 Location Central US Number of non service operations 97,960 Number of in service tap changes 22,465 Date of inspection 21-Oct-12

2 Introduction The type VRLTC pilot was applied on a 56 MVA top rated power transformer manufactured by Federal Pacific in The type VRLTC replaced a Federal Pacific type TC-25 load tap changer. Existing leads from the transformers regulating winding and preventative autotransformer were used to connect the transformer to the type VRLTC. The type VRLTC was welded on the transformer and was energized in January The tap changer was monitored remotely by ABB tap changer engineers during its time in service. After nine months of customer service and 22,465 operations under load, the type VRLTC was opened for inspection during a planned outage at the substation which occurred during the week of October 21st, Initially, the voltage bandwidth was intentionally narrowed to accelerate the number of tap change operations the pilot VRLTC would experience per day. At the time of inspection, the total number of operations on the type VRLTC pilot had exceeded 120,000. Inspection Results The pilot VRLTC was thoroughly and extensively inspected by qualified tap changer service technicians and engineers along with the utility s engineering and operations supervisors. The results of the inspection are detailed in this section. Inspection of the type VRLTC motor drive Tap Logic Monitoring System (TLMS) event log review The TLMS is an advanced, microprocessor based monitoring and control system for the type VRLTC tap changer. Figure 2 shows the TLMS of the VRLTC which was under inspection. In addition to its monitoring and controlling functions, the TLMS acquires and stores data for each tap change, including any significant events which may occur to the tap changer. The data can be downloaded to a laptop from the USB port integrated into the swing panel of the motor drive. During the pilot VRLTC inspection, no alert or alarm conditions were present on the TLMS vacuum fluorescent display or in the event log. This information indicates that no issues existed during nine months of operation. The TLMS event log was downloaded to provide information relating to the conditions that the tap changer experienced while in operation. Each event or condition that is logged into the TLMS memory also has a corresponding time stamp. This allows the user to determine what event occurred and when the event occurred. Figures 3-8 provide detailed information acquired from the download of the TLMS event log. Figure 1 Motor drive operations counter exceeding 120,000 operations. Figure 2 TLMS mounted in the type VRLTC pilot motor drive. Note the amber light above TLMS indicates the VRLTC is in no-load mode. No-load mode allows the user to disable some monitoring features of the TLMS, which will allow the user to operate the VRLTC while the transformer is de-energized without a lock out alarm. For safety resasons, No-load mode can only be entered when the transformer is de-energized. 2 VRLTC load tap changer Pilot inspection report

3 Tap range over time 17 Tap Position /27 2/10 2/24 3/9 3/23 4/6 4/20 5/4 5/18 6/1 6/15 6/29 7/13 7/27 8/10 8/24 9/7 9/21 10/5 10/ Figure 3 Tap range over time. Note that the pilot VRLTC mostly operated in the lower tap range and infrequently used the reversing switch due to the customer s system operation. Time based operation of the type VRLTC reversing switch is not required. Tap Position Tap changes on daily basis # of tap changes performed per day Total number of tap changes performed # of tap changes performed per day Total number of tap changes performed 1 0 Figure 4 Number of tap changes performed per day. Note that initially the voltage bandwidth was intentionally narrowed to accelerate the number of tap change operations the pilot VRLTC would experience per day. In March, the voltage bandwidth was returned to a normal setting for a load tap changer. Pilot inspection report VRLTC load tap changer 3

4 Number of bypass operations Upper bypass, P2 Lower bypass P3 6,948 31% Upper bypass P3 15,518 69% Lower bypass, P3 Figure 5 - Bypass operations chart and bypass switch. Note that 69% of tap change operations occurred using the P2 bypass switch. This data can allow the user to assess which bypass mechanism parts will not require replacement prior to a planned maintenance on the VRLTC. Internal temperature versus ambient Average daily temperature inside motor drive enclosure Average daily temperature Temperature ( F) Date Figure 6 Motor drive compartment temperature versus ambient temperature. Note that the ambient temperature inside the motor drive is well within the acceptable range of the motor drive components, including the digital components. The safe operating temperature range for all motor drive components is -40 F to 176 F. Ambient temperature data was acquired from a local weather station. 4 VRLTC load tap changer Pilot inspection report

5 Internal humidity versus ambient humidity Relative Humidity 100% 95% 90% 85% 80% 75% 70% 65% 60% 55% 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Average Daily RH% Inside Motor Drive Enclosure Average Daily RH% in West Lafayette (Station 30692) Date Figure 7 Motor drive relative humidity versus ambient relative humidity. Note that the TLMS is actively controlling the humidity inside the motor drive enclosure by operating the heater as needed. Proper control of humidity mitigates the formation of corrosion inside the motor drive enclosure. Ambient relative humidity data was acquired from a local weather station. Percentage of time spent on each tap position 25% % of time on tap position 20% 15% 10% 5% 0% 16L 15L 14L 13L 12L 11L 10L 9L 8L 7L 6L 5L 4L 3L 2L 1L N 1R 2R 3R 4R 5R 6R 7R 8R 9R 10R11R12R13R14R15R16R Figure 8 - Percent of time on tap position. Note that this data can be used to determine how long the VRLTC contacts have been on one position. Furthermore, it provides information which can be used prior to a maintenance event which will allow the user to reduce the number of components required for maintenance and order only the components which will be required for the maintenance event. Pilot inspection report VRLTC load tap changer 5

6 Torque inspection of the servo motor The type VRLTC motor drive uses a brushless AC servo motor as opposed to an induction motor. Utilizing the data acquisition and storage features of the type VRLTC motor drive, the torque data for a tap change was quickly acquired. Torque data was collected for the entire tap change range (16L-N-16R). The pilot torque profile was then compared to the standard torque profile of a type VRLTC (Figure 9). There was a maximum torque deviation of 2.3% from the standard torque profile. This data provided quick confirmation that there were no mechanical issues with the type VRLTC pilot. Torque vs. time Pilot Unit Typical Figure 9 Torque versus time. This plot shows the type VRLTC torque signature for a single reversing switch operation taken at the substation (1L-R) in dark blue versus the standar type VRLTC torque signature in light blue. Multi-turn absolute encoder The multi-turn absolute encoder is a device which precisely communicates the tap position to the TLMS. As opposed to electromechanical cam switches, the multi-turn absolute encoder uses optical discs for position acquisition. The optical discs are fully sealed within the metal case of the device. No cam switches are used in the type VRLTC motor drive, so there was no need for inspection or maintenance of these maintenance-prone devices. During the pilot inspection, the non volatile memory function of the multi-turn absolute encoder was tested by simulating a power failure during a tap change. The multi-turn absolute encoder was found to be working perfectly. Figure 10 shows the multi-turn absolute encoder in the pilot VRLTC motor drive. Figure 10 Picture of the multi turn absolute encoder in the pilot VRLTC motor drive enclosure. With the only exception being the TLMS, every component in the VRLTC motor drive, including the multi-turn absolute encoder, is commercially available from multiple domestic suppliers. 6 VRLTC load tap changer Pilot inspection report

7 Inspection of the VRLTC active part Oil Analysis Oil samples were taken from the sampler port of the drain valve at the bottom of the tank. The oil was tested by Doble Engineering for dissolved metals, moisture content, Dielectric (D877), and power factor at 25C. Monthly oil samples were taken by the utility for dissolved gas analysis to monitor the performance of the type VRLTC. Following the inspection of the tap changer, the same oil which had been drained was used to refill the type VRLTC. Figure 11 provides a summary of the oil quality tests for the oil taken from the sampler port prior to draining the tap changer. The oil was found to be in great condition with no detectable traces of dissolved metals in the oil. Type VRLTC pre-inspection oil quality tests - Sample acquired October 22, 2012 Report # Sample date Top oil temp. C Water content Relative saturation Diel D877 PF25C /22/ ppm 55 kv 0.024% Fe Cr Pb Cu Sn Al Ni Ag Mo Ti Si Mg Zn W ND ND ND ND ND ND ND ND ND ND ND ND ND ND Figure 11 Pre-inspection oil quality tests Tap selector and reversing switch inspection The mechanical motion of the pilot VRLTC was observed by using the jog mode. Jog mode is a test mode in the TLMS which allows the user to significantly slow the tap change speed and thoroughly inspect all mechanical motion of a tap change. Each phase of the type VRLTC tap selector and reversing switch were inspected for contact wear and proper sequencing during the inspection. Figure 12 shows the selector moving fingers and stationary contacts. The amount of silver deposited onto the stationary contacts indicates proper function of the selector. The silver on silver contact lowers contact resistance which mitigates losses and excessive heat generation. Figure 13 shows the reversing switch moving contacts and stationary contacts. The type VRLTC selector and reversing contacts were found to be in a like new condition. Figure 14 shows the contact motion being observed while in jog mode. Figure 12 Selector moving contacts of pilot VRLTC Pilot inspection report VRLTC load tap changer 7

8 Figure 13 Reversing switch moving contact of pilot VRLTC Figure 14 While in jog mode, the moving contacts were positioned for a quick inspection during a tap change Diverter inspection - bypass switch The type VRLTC bypass switch was designed as a robust and maintenance free switch. The bypass contacts provide cleaning or wiping motion at contact points and generous temperature rise margins to mitigate the possibility of the formation of pyrolytic carbon (which leads to contact coking). Micro ohm measurements were taken across the bypass contact bundles. Figure 16 provides a table of the micro ohm test results for the bypass switches. From the results, we can conclude that the bypass switches are in like-new condition. Bypass µ-ohm test results for pilot unit Left phase (µω) Center phase (µω) Right phase (µω) Measured Nov Upper bypass (P2) Lower bypass (P3) Measured Oct Upper bypass (P2) Lower bypass (P3) Figure 16 Table comparing bypass switch micro ohm test results taken in November, 2011 and October, Diverter inspection - vacuum interrupters The type VRLTC uses vacuum interrupters designed to withstand the harshest environments for load tap changers. The vacuum interrupter mechanism for each diverter was fully tested for moving contact displacement, opening and closing velocities, and contact bounce against production parameters for a new diverter in both the raise and lower directions. All three diverters met the criteria to be considered new. There was no measurable erosion of vacuum interrupter contacts. The vacuum interrupters were Hipot tested per manufacturer s recommendations at 14 kv and 60 Hz for 1 minute and no discernible current flow was measured through the open contacts. Micro ohm measurements were taken across the vacuum interrupter contacts. Figure 17 provides a table of the micro ohm test results for the vacuum interrupters. VI micro ohm test results for pilot unit Phase tested Vacuum interrupter New Units Right phase µohm Center phase µohm Left phase µohm Figure 17 Table of vacuum interrupter micro ohm test results. 8 VRLTC load tap changer Pilot inspection report

9 Timing and sequencing inspection A summary of the timing and sequencing analysis for a tap change cycle is provided in Figure 18. After more then 120,000 operations, the pilot VRLTC yielded no deviation in timing or sequencing. All parameters were satisfied for the pilot VRLTC to meet production level standards to be considered a new unit. Steady state on bridging position Open by-pass Open VI Open Selector 0 time = 0 s Close Selector Steady state on on new position Close VI Close by-pass non bridging position 196 Figure 18 Timing and sequencing testing summary time = 2.0 s Inspection of VRLTC accessories All of the pilot VRLTC accessories were inspected and tested according to the manufacturer s recommendations. A summary of the accessory inspection is listed in Figure 19. Conclusion After a thorough and extensive review of all the components that create the type VRLTC, the unit is considered to be in a like new condition. In addition, no alert or alarm was present on the TLMS display or in the event log. Based upon our analysis, it is our conclusion that the pilot VRLTC has experienced no loss of service life during its time of operation. There is no further need for inspection until the pilot VRLTC reaches the normal inspection requirement at 500,000 operations. Marketing Contacts Jon Brasher Technical Specialist and Sr. Account Executive (731) jon.c.brasher@us.abb.com Randy Williams Utilities Segment Manager (731) randy.williams@us.abb.com Pilot inspection report VRLTC load tap changer 9

10 For more information please contact: ABB Inc South Cavalier Drive Alamo, Tennessee 38001, USA Phone: Fax: Note: We reserve the right to make technical changes or modify the contents of this document without prior notice. The information, recommendations, description and safety notations in this document are based on our experience and judgment. This information should not be considered all inclusive or covering all contingencies. ABB does not accept any responsibility whatsoever for potential errors or possible lack of information in this document. If further information is required, ABB should be consulted. We reserve all rights in this document and in the subject matter and illustrations contained therein. Any reproduction in whole or in parts is forbidden without prior written consent from ABB. 1ZUA With regard to purchase orders, the agreed particulars shall prevail. In no event will ABB be responsible to the user in contract, in tort (including negligence), strict liability or otherwise for any special, indirect, incidental, or consequential damage or loss whatsoever including but not limited to use of equipment, plant or power system, cost of capital, profits or revenues, cost of replacement power, additional expenses in the use of existing power facilities, or claims against the user by its customers resulting from the use of the information, recommendations, description and safety notations contained herein. Copyright 2013 ABB. All rights reserved.