The Next Generation in Surge Suppression

Transcription

1 Western Mining Electrical Association November 16 th 18 th, 2005 The Next Generation in Surge Suppression Ted Arbuckle Raycap Corporation 1 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

2 Introduction Power Surges the Problem Transient Voltage Surge Suppression Principles of Operation Conventional TVSS Designs Consequences of Failure An Engineered Remedy Conclusions 2 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

3 Why Install a Transient Voltage Surge Suppressor Transient Voltage Surge Suppressors are provisioned to protect electrical equipment from damaging surges. Electronic equipment such as VSD s, SM Power Supplies, and Computers have become more sensitive to surges as their efficiency has increased and the size and weight of the devices has decreased. We rely on electronic equipment to protect mission critical and production facilities from service interruptions. Down time is not an option! 3 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

4 TVSS Operation TVSS :A device which limits the voltage within an acceptable range: Positive Spike Oscillatory Surge Positive Notch Let-through Voltage Voltage Voltage Swell Negative Spike The ideal TVSS should: Absorb all energy above a preset voltage level and safely dissipate it. Not cause interruption of the normal function of the load Be reliable and work consistently without wearing out. 4 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

5 Suppression Components 5 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

6 Parallel Metal Oxide Varistors - MOV s 6,000A impulse 30,000A impulse 6 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

7 Why Do Protectors Fail? Poor mechanical and electrical design. Parallel, low rated devices assume equal current sharing and perfect matching during life time. Weak fusing 7 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

8 Why Do Protectors Fail? 8 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

9 Thermal Runaway New device Aging OR AC power surge for several cycles causes heating and thermal runaway Clamp voltage drops Device Heats Failure Current limiting and thermal fuses are being used to prevent thermal runaway. This fusing becomes the limiting factor for the suppression technology. 9 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

10 Parallel MOV s Most TVSS devices use many metal oxide varistors (MOV's) connected in parallel in an attempt to achieve the required levels of performance. Different MOV s have different turn on voltages and different ageing patterns resulting in unpredictable performance after installation. They don t share current equally, and performance degrades when one MOV handles a large current surge. 10 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

11 Why Protect the Protector? Rupture due to large electromagnetic forces generated by high current lightning surge Degradation in clamping performance due to ageing, and unequal surge current sharing Burning due to degradation in clamping voltage and thermal runaway 11 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

12 Why Does Protection Fail Supply Fuse Line 30A internal fuse Load Conventional TVSS Neutral/Ground 1. Voltage on load equals protector voltage plus fuse voltage plus cable voltage. This can add thousands of volts to the protection level. 2. Operation of the fuse generates significant voltage across the load. Load is left unprotected for the next strike. 3. End of life mode is an open circuit. 12 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

13 Why Do Protectors Fail? Lack of, or inappropriate testing. Extensive use of varistor math. Misinterpretation of UL tests 3 Lab tests do not represent actual installations (lead length, point of measurement). Fusing. Overcurrent fuses are often underrated to protect the TVSS. Conventional thermal fuses are unreliable and suffer from aging. Fuse operation generates surge that may damage load. 13 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

14 Why Does Protection Fail? Conventional installation can render protector useless. Protector ratings do not allow in line connection. Long lead lengths cause large inductive voltage to appear across the load. Fuse operation disconnects the protection and leaves the load exposed. 14 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

15 Consequence of Failure TVSS damage or destruction. Emission of gases, smoke and soot. Switchgear contamination by smoke and soot. Explosions, fires. Protected equipment damage Down Time $$$ 15 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

16 Protector Requirements The load should never be exposed to damaging transients/surges whatever the condition of the protector. The protector poses no additional safety risks e.g. Smoke, fumes, fire and explosion. The reliability and lifetime of the protector is greater than the equipment/load being protected. Installation should not affect the ability of a protector to perform its intended function. The protector should be able to deal with all abnormal line conditions and provide protection at all times. 16 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

17 Protector Features No flammable material should be used in construction. Must be physically robust and not have an explosion hazard. Should require no internal fusing. Should have safe end of life, e.g. short circuit. Must be capable of installation using the Kelvin method. Must have a long life. Able to dissipate absorbed surge energy safely without undue heating. Must have low internal dynamic impedance. 17 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

18 The Engineered Protector Large Thermal Capacity Electrodes Strong Aluminum Housing Pounds of Pressure No Fuel to Burn Low Dynamic Resistance & Low Residual Voltage Single, Distribution-Grade Varistor No Parallel MOVs Fuseless Operation 18 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

19 Conventional Protection Line /Phase Supply LOAD 30 to 80 A local fuse TVSS Neutral/Ground/Return 19 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

20 Total Protection Line /Phase Supply TVSS LOAD Neutral/Ground/Return 20 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

21 The Engineered Protector Let through Voltage at intremediate surge currents Voltage (V) Surge current at 8/20µs (ka) Strikesorb Parallel MOV 21 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

22 Optimum In Line Installation Optimum installation Line Main Breaker In-Line Connection VSD Neutral / Ground 22 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

23 Tested, Not Calculated, Performance Energy handling: 250 x 2000µs High current impulses: 200kA - 8/20µs 100 x 65kA 8/20µs 2000 x 20kA 8/20µs 25kA 10/350µs Dynamic resistance: < 5mΩ 23 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.

24 Conclusions It is possible to provide the correct protection even in the most extreme conditions. Fire and explosions can be prevented using good engineering practice. It is possible to provide protection that never gives up and never exposes equipment to excess energy. 24 Copyright 2005 Electric Power Research Institute, Inc. All rights reserved.