WO2010070403A1

WO2010070403A1 - An overvoltage protection assembly for medium voltage wind turbines

Info

Publication number: WO2010070403A1
Application number: PCT/IB2009/007490
Authority: WO
Inventors: Kevin L. Cousineau; Hanif Mashal
Original assignee: Clipper Windpower, Inc.
Priority date: 2008-12-17
Filing date: 2009-11-18
Publication date: 2010-06-24
Also published as: TW201030773A

Abstract

An overvoltage protection assembly, which includes a grounding plate (40), a mechanical standoff including two upright insulated or non-conducting supports (26, 28) and a conducting member providing a bridge (30) spanning the supports. The mechanical standoff is secured to a top surface of the grounding plate and is insulated from the grounding plate. A plurality of overvoltage-protection modules (10) are connected to each other in series. A first module (11) in the series is fixed in place on the top surface of the grounding plate and the last module (15) in the series is fixed in place on a bottom surface of the bridge (30). The overvoltage protection assembly is replicated on the grounding plate for each of three phases (50) of service to a power grid and three cables (52, 64, 66) connect each conducting member to a corresponding phase. A single cable (56) connects the grounding plate to a common grounding bar (60).

Description

AN OVERVOLTAGE PROTECTION ASSEMBLY FOR MEDIUM VOLTAGE WIND

TtJRBINES

FIELD OF THE INVENTION The present invention relates to voltage surge protection devices and, more particularly, to means for mounting stacked overvoltage protection modules.

BACKGROUND OF THE INVENTION Frequently, excessive voltage occurs across the power lines of a power transmission grid to which a wind power source delivers power. Such excess voltage or voltage surges may result from lightning strikes or other causes. The voltage surges are of particular concern to wind turbines where equipment damage caused by voltage surges and resulting down time may be very costly.

Typically, one or more varistors (i.e., voltage dependent resistors) are used to protect a wind turbine from voltage surges. Generally, the varistor is connected directly across the AC power lines and in parallel with the protected circuit. The varistor has a characteristic clamping voltage such that, responsive to a voltage increase beyond a prescribed voltage, the varistor forms a low resistance shunt path for the overvoltage current that reduces the potential for damage to the sensitive components. Typically, a line fuse may be provided in the protective circuit and this line fuse may be blown or weakened by the essentially short-circuit created by the shunt path.

Currently, low voltage (2.5MW) turbines use the fuseless Raycap Strikesorb LVtm modules which provide a high level of protection against lightning and surge currents compared to conventional Transient Voltage Surge Suppressor (TVSS) arrays with internal fuses. Those modules incorporate a robust industrial grade metal oxide varistor (MOV) in a cylindrical aluminum housing. These modules provide a further advantage in that they preserve their performance characteristics for several years with multiple lightning and power surge events.

It is therefore desirable to provide the same protection as available for low voltage turbines in setups with medium voltage wind turbines .

It is an object of the invention to provide an overvoltage protection assembly which can be used in medium voltage turbines .

SUMMARY OF THE INVENTION Previously there was no directly connected metal oxide varistor (MOV) available in the market for medium voltage turbines. The available medium voltage TVSS uses internal series fuses .

According to the invention, metal oxide varistors (MOV) are used in conjunction with the main medium voltage circuit breaker in the power distribution panel in order to provide a secure and robust overvoltage protection device. This setup comprises an apparatus of fuseless stacked MOVs (Metal Oxide Varistors) in conjunction with the upstream circuit breaker (direct connection) in medium voltage wind turbines for the purpose of lightning strikes and surge current protection. The assembly according to the invention does not require an internal fuse to operate safely. Cables can be attached directly to the internal bus bars of the OV modules, eliminating the voltage drop across a fuse. The advantages are lower clamping voltages, elimination of voltage surge when a fuse opens, lower maintenance and no parts to replace.

As suitable MOVs the multi-Strikesorbtm modules may be used, since they provide the required protection level with a direct connection. The invention comprises an overvoltage protection assembly including a mechanical standoff having one or more upright supports and a conducting member providing a bridge spanning the supports. The mechanical standoff is secured to a top surface of a grounding plate and insulated from the grounding plate. A plurality of overvoltage protection modules, each containing Metal Oxide Varistors, are connected to each other in series, a first module in the series being fixed in place on the top surface of the grounding plate and a last module in the series being fixed in place on a bottom surface of the bridge.

The invention has the advantage that the series connected modules offer superior performance in terms of surge rating and safety in comparison with conventional series fused type Transient Voltage Surge Suppressors. The application of these modules offers the best possible protection against lightning strikes and surge currents for medium voltage wind turbines, without raising any safety issues for the operation of the wind turbine. It also provides a cost effective improvement.

According to the invention, a conventional voltage circuit breaker is used in combination with the MOV setup in order to provide protection in situations in which the MOVs are not triggered. Further do the MOV stacks in their standoffs protect the voltage circuit breaker from damage under fault conditions which can not be handled by the voltage circuit breaker but are severe enough to trigger the MOV stacks .

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings :

FIGURE 1 is a bottom, perspective view of an overvoltage protection module 10;

FIGURE 2 is a perspective view of mechanical standoff with two non-conducting supports according to embodiments of the present invention;

FIGURES 3a- 3d are views of the overvoltage protection module of FIGURE 1 mounted in the mechanical standoff of FIGURE 2, wherein the subassembly includes three overvoltage protection modules in series ;

FIGURE 4 is a perspective view of a grounding plate forming a part of the overvoltage protection subassembly of FIGURE 3 wherein three modules are connected in series;

FIGURE 5 is a perspective view of a grounding plate forming a part of the overvoltage protection subassembly of FIGURE 3 wherein four modules are connected in series,-

FIGURE 6 is a perspective view of the grounding plate subassembly of FIGURE 4 mounted within a power distribution panel; and

FIGURE 7 is a schematic wiring diagram of a generator system in which the invention is embodied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overvoltage Protection Module

Refer to FIGURE 1, which is a bottom, perspective view of an overvoltage protection module 10. Suitable overvoltage protection modules include the Raycap Strikesorb TM Transient Voltage Surge Suppressor (TVSS) .

The overvoltage protection module 10 includes a housing of generally cylindrical shape. The housing has an end wall 12, a cylindrical wall 14 extending from the end wall 12, and a threaded stud bolt 16 extending from the lower surface of the end wall 12. The cylindrical wall 14 and the end wall 12 form an interior cavity. The protection mechanism is located within the cavity. A threaded bore is formed in the end of the shaft 18 and is modified by the present invention to receive a bolt 16 of a similar module 10 such that a number of modules can be threaded to each other in series as shown in FIGURE 3. An insulator ring 20 is provided.

Standoff System

Refer to FIGURE 2, which is a perspective view of mechanical standoff 24 according to the present invention. The mechanical standoff system 24 includes at two upright non-conducting supports 26, 28 and a conducting member providing a bridge 30 spanning the supports. The bridge 30 has a bore 32 with an internal diameter that will accept the shaft 18 of the module 10. The upright supports have insulation at their respective distal ends 34, 36. The distal ends 34, 36, are threaded to accept bolts.

Standoff System and Module Sub-assembly

Refer to FIGURE 3a-3d, which are views of a mechanical standoff 24 designed to accept three modules in series. The mechanical standoff 24 includes at two upright non-conducting or insulated supports 26, 28 and a conducting member providing a bridge 30 spanning the supports. The bridge 30 has a bore 32 with an internal diameter that will accept the shaft 18 of the top module in the series. A bolt 38 secures the top module to the bridge 30. The upright supports may have insulation at their respective distal ends 34, 36. The distal ends 34, 36, are threaded to accept bolts.

The supports 26, 28 may be constructed of non-conducting material or conducting material with insulation, so long as the bridge 30 is insulated from the grounding plate 40 described below.

Grounding Plate

Referring to FIGURE 4 and FIGURE 5, a grounding plate 40 is provided. The grounding plate has a top surface 42. Threaded bores 44 are cut through the grounding plate. The bores are adapted to receive the threaded stud 16 of the bottom overvoltage protection module 10 in a series of three modules 10 shown in FIGURE 4 or a series of four modules 10 shown in FIGURE 5. It will be understood by those skilled in the art that the supports 26, 28, must be appropriately resized to accommodate the four modules 10 shown in FIGURE 5.

An additional bore 46 is provided to receive a bolt of a ground wire connection as discussed below. The grounding plate is formed of an electrically and thermally conductive material. For example, the material may be aluminum, steel, brass or copper. The proximate ends of the upright supports 28, 28 are bolted to the bridge 30. The distal ends of the upright supports 28, 28 are bolted to the top surface 42 of the grounding plate 40 by passing bolts through holes 48.

The overvoltage protection module 10 is mounted on the top surface 42 of the grounding plate 40, by screwing the threaded stud 16 into the threaded bore 44 of the grounding plate. The overvoltage protection module 10 is screwed in until the bottom surface 12 securely abuts the top surface 42 of the grounding plate so as to secure the overvoltage protection module 10 in place.

Power Distribution Panel (PDP)

Refer to FIGURE 6, which is a perspective view of the grounding plate subassembly of FIGURE 4 mounted within a power distribution panel (PDP) . The three phases 50 from the turbine generators pass through a service disconnect switch 52 and from- thence to a grid tie-in point 54, which connects to a utility grid.

The three bridges 30¹Of each of three replicated standoff systems are attached in parallel with the three phases by means of three cables 62, 64, 66. A ground line 56 is secured to the grounding plate 40 by means of a lug and bolt 58. The ground line is connected to a common grounding copper bar 60.

In the event of an overvoltage condition, the resistance of the varistor wafer in module 10 decreases rapidly, allowing current to flow through the module 10 and create a shunt path for current flow to protect other components of the electrical system. Each overvoltage protection module 10 is mounted on a respective one of the standoffs and has a respective service line 62, 64, 68 connected to the respective bridge 30 thereof. Circuit Diagram

Refer to FIGURE 7, which is a schematic wiring diagram of the service of FIGURE 4 within a generator system connected to a power grid. The turbine comprises rotor blades connected to a turbine main- shaft, which transmits the turbine's mechanical torque via a torque reducing gear box to 4 high speed shafts 70 and via a suitable coupling device the high speed shafts are coupled to four permanent-magnet or wound field synchronous generators 72, 74, 76, 78 The generator electrical output is connected to the rectifiers, 78, 80, 82, and 84, which convert the electrical AC output power of the generator to DC voltage and current. The DC power is then transmitted to inverters 86. The inverter 86 regulates its AC out put current to the gird and by doing so, the generator torque is controlled. The inverter regulates this AC output current while synchronizing itself to the grid voltage and also capable of supplying unity power factor current into the grid system. The control of the inverters is provided by a generator control unit (not shown) .

Power 50 is passed through a power distribution panel 87 wherein the three replicated standoff systems 24 are attached in parallel with the three phases 50 by means of three cables 62, 64, 66. Power is passed through a medium voltage circuit breaker 67 to a pad-mount transformer 88, which is connected to a grid 90.

The invention has been illustrated in the drawings by three and four overprotection modules 10 in series. It will be understood by those skilled in the art that the overprotection assembly can be sized to accommodate one overvoltage protection module fixed in place on the top surface 42 of the grounding plate 42 and on the bottom surface of the bridge 30. Similarly, the overprotection assembly can be sized to accommodate two overvoltage protection modules, a first module fixed in place on the top surface 42 of the grounding plate 40 and a second module connected in series with the first module and fixed in place on the bottom surface of the bridge 30.

Claims

C l a i m s1 . What is claimed is :

1. An overvoltage protection assembly comprising: a grounding plate 40; one or more overvoltage protection modules 10 connected to each other in series; a mechanical standoff including an upright support 26 and a conducting member providing a bridge 30 spanning said support 26 and said overvoltage protection modules 10, said mechanical standoff being secured to said top surface 42 of said grounding plate 40 and insulated 34 from said grounding plate, and a last module 15 in said series of modules 40 being fixed in place to a bottom surface of said bridge 30 and in electrical contact with said bridge; wherein the overvoltage protection modules are connected to each other in series, such that a first module 11 in said series of modules 10 being fixed in place on a top surface 42 of said grounding plate 40 and in electrical contact with said grounding plate .

2. An overvoltage protection assembly, said assembly comprising: a grounding plate 40; a mechanical standoff including one or more upright supports 26, 28 and a conducting member providing a bridge 30 spanning said supports, said mechanical standoff being secured to a top surface 42 of said grounding plate 40 and insulated 34 from said grounding plate,- and one or more overvoltage protection modules which are connected to each other in series, a first module in said series being fixed in place on said top surface 42 of said grounding plate and a last module in said series being fixed in place on a bottom surface of said bridge 30.

3. The assembly in accordance with claims 1 and 2 wherein said mechanical standoff includes one or more upright supports, said conducting member providing a bridge spanning said supports, said mechanical standoff being secured to a top surface of said grounding plate and insulated from said grounding plate .

4. The assembly in accordance with claims 1, 2 and 3 wherein each mechanical standoff 26, 28 s insulated from said grounding plate 40.

5. The assembly in accordance with claims 1, 2 and 3 wherein each mechanical standoff 26, 28 is constructed of nonconducting material.

6. The assembly in accordance with claims 1, 2, 3, 4 and 5 wherein said one or more overvoltage protection modules 10 comprise one overvoltage protection module fixed in place on said top surface 42 of said grounding plate and said bottom surface of said bridge 30.

7. The assembly in accordance with claims 1, 2, 3, 4 and 5 wherein said one or more overvoltage protection modules 10 comprise two overvoltage protection modules connected to each other in series.

8. The assembly in accordance with claims 1, 2, 3, 4 and 5 wherein said one or more overvoltage protection modules 10 comprise three overvoltage protection modules connected to each other in series.

9. The assembly in accordance with claims 1, 2, 3, 4 and 5 wherein said one or more overvoltage protection modules 10 comprise four overvoltage protection modules connected to each other in series.