diode fault detector

8/10/2019 Diode Fault Detector

1/29

351-02020-01A

INSTRUCTION MANUAL

Diode Fault Detector

for Series Redundant Brushless Exciters

Description Installation Operation Maintenance Parts Description

Made By:

Rockwell Automation - P.O. Box 8446Kato Engineering Mankato, MN 56002-8447(507) 625-4011Fax. (507) 345-2798


2/29

DANGER

ONLY QUALIFIED PERSONNEL FAMILIAR WITH THE CONSTRUCTION ANDOPERATION OF THIS EQUIPMENT AND THE HAZARDS INVOLVED SHOULDINSTALL, ADJUST, OPERATE AND /OR SERVICE THIS UNIT. READ ANDUNDERSTAND THIS MANUAL IN ITS ENTIRETY BEFORE PROCEEDING. FAILURETO OBSERVE THIS PRECAUTION COULD RESULT IN SEVERE BODILY INJURY OR LOSS OF LIFE.

DANGER

THE USER IS RESPONSIBLE FOR CONFORMING TO THE NATIONAL ELECTRICCODE AND ALL OTHER APPLICABLE LOCAL CODES. WIRING, GROUNDING,DISCONNECTS, AND OVERCURRENT PROTECTION ARE PARTICULARLYIMPORTANT. FAILURE TO OBSERVE THIS PRECAUTION COULD RESULT INSEVERE BODILY INJURY OR LOSS OF LIFE.

DANGER

SUBSEQUENT STEPS REQUIRE ROTATING PARTS AND/OR ELECTRICAL CIRCUITSTO BE EXPOSED. STAY CLEAR IF UNIT MUST BE RUNNING OR DISCONNECT ANDLOCKOUT AND TAG POWER SOURCE IF CONTACT MUST BE MADE. FAILURE TOOBSERVE THESE PRECAUTIONS COULD RESULT IN SEVERE BODILY INJURY OR LOSS OF LIFE.

WARNING

IF LIFTING OF EXCITER IS REQUIRED, DO NOT PULL AT AN ANGLE ON LIFTINGEYES. THE LIFTING EYES ARE FOR THE UNIT ONLY AND NOT FOR THECOMPLETE SET. FAILURE TO OBSERVE THESE PRECAUTIONS COULD RESULT INBODILY INJURY.


3/29

Table of Contents

SECTION 1: Introduction and Description

1.1. Introduction1.2. General Description1.3. Construction and Mounting

1.3.1. Diode Fault Detector (DFD) Versions and Application1.3.2. Input Connections1.3.3. Output Connections1.3.4. Installation Instructions

1.3.4.1 508-00118-31, -32 Detectors1.3.4.2 508-00118-33 Detectors

1.4 Description of Operation1.4.1. DFD Circuit Overview

1.4.2. DFD Output Signals

SECTION 2: Initial Inspection, Storage and Alignment

2.1. Receiving Inspection2.2. Alignment and Adjustments

SECTION 3: Maintenance

3.1 Periodic Maintenance3.2 Replacement3.3 Insulation Resistance

SECTION 4: Troubleshooting

4.1. Diode Fault Alarm4.2. Troubleshooting General Method4.3. Wire Continuity Test4.4. Checkout of Signal Wires to Ground Detector 4.5. Functional Check of Diode Fault Detector 4.6. Replacement Part Numbers


4/29

TABLE OF FIGURES AND ILLUSTRATIONS

Figure 1: Diode Fault Detector Mounting on Brushless Exciter Rotors

Figure 2: Block Diagram of Detector AC and DC Connections on Diode Wheel

Figure 3: Complete Diode Wheel Assembly (6A6 and 7A6 type exciter designs)

Figure 4: Diode Wheel Assembly Inboard Side (6A6 and 7A6 type exciter designs)

Figure 5: Diode Wheel Assembly Outboard Side (6A6 and 7A6 type exciter designs)

Figure 6: Diode Fault Detector Outline of Mounting and Connections

Figure 7: Diode Fault Detector Mounting Face View (Photo)

Figure 8: Diode Fault Detector Top View and Output Connections to Ground Detector System(Photo)

Figure 9: Diode Fault Detector Connection Example to DC Buss (Photo of 6A6 and 7A6 typeexciter designs)

Figure 10: Diode Fault Detector AC Connection Example and Wire Harness Securing in DiodeWheel Groove (Photo of 6A6 and 7A6 type exciter designs)

Figure 11: Complete Diode Wheel Assembly (7A7 and 9A4 type exciter designs)

Figure 12: Diode Wheel Assembly Inboard Side (7A7 and 9A4 type exciter designs)

Figure 13: Diode Wheel Assembly Outboard Side (7A7 and 9A4 type exciter designs)

Figure 14: Block Diagram of Diode Fault Detector / Field Ground Detector

Figure 15: Diode Fault Detector Alarm Logic


5/29

1. INTRODUCTION AND DESCRIPTION

1.1 Introduction

This manual describes the Diode Fault Detector used on brushless exciters with series redundant diodes on the diodewheel used mainly on 2 pole synchronous generators. The instruction book covers the general description,construction, installation, operation, initial inspection, maintenance, troubleshooting and renewal parts.

1.2 General Description

The Diode Fault Detector is used in conjunction with a field ground detector system (see separate instruction book)to detect faulty diodes in a series redundant brushless exciter system. The brushless excitation system consists of ahigh frequency AC generator complete with a rotating, series redundant diode assembly and a lead assembly thatconnects the DC diode bridge output to the field windings of the main generator. The Diode Fault Detector is aelectronic module mounted underneath the rim of the diode assembly hub or wheel between the wheel and the

armature of the exciter as shown in Figure 1.The module connects to the AC and DC connections of the rectifier bridge and monitors the forward voltage drop of the series redundant diodes within the rectifier bridge. It is also powered from the DC connections. If a diode failsopen or shorted , the forward voltage drop of the cells in that leg changes with respect to the other legs of the bridge.This creates a ripple in the forward voltage balance which is detected in the module. When the ripple exceeds a

preset threshold, the module sends a fault signal to the field ground detector transmitter (see separate instruction book) located diametrically opposite the Diode Fault Detector. The transmitter in turn sends the alarm signal to astationary receiver unit. The receiver sends this alarm signal to a remote device such as the brushless exciter voltageregulator which provides a fault signal to the user.A block diagram of how the Diode Fault Detector connects to the exciter and ground detector system is shownin Figure 14 (found in section 1.4.).


6/29

FIGURE #1b: DIODE FAULT DETECTOR MOUNTING

(CUT AWAY VIEW)

DIODE WHEEL ASSEMBLY

WIRE HARNESS GROOVE

TRANSMITTER

AC CONNECTION LINKS

DFD OUTPUT CONNECTIONS

AC CONNECTION RING

TO GROUND DETECTORGREEN

DIODE FAULT DETECTORRED

(7A7 AND 9A4 TYPE BRUSHLESS EXCITER ROTORS)

SPACER

FIGURE #1a: DIODE FAULT DETECTOR MOUNTING

DIODE FAULT DETECTOR

DIODE WHEEL ASSEMBLY

WIRE HARNESS GROOVE

AC CONNECTION RING

DFD OUTPUT CONNECTIONS TO GROUND DETECTOR

RED

AC CONNECTION LINKS

GREEN

TRANSMITTER

(CUT AWAY VIEW)

(6A6 AND 7A6 TYPE EXCITER ROTOR DESIGNS)


7/29

1.3 Construction and Mounting

The Diode Fault Detector (DFD) is consists electronic components mounted to printed circuit boards and a heat sink which are encapsulated in a high strength molded potting compound. The Detector has 2 holes for mounting to theface of the diode assembly as shown in Figures 3 to 6.

1.3.1. DFD Versions and Application

As of the date of this publication there are 4 models of Diode Fault Detectors. These models are used for various DC buss operating voltages and different diode wheel mechanical arrangements. The following listgives the Kato Engineering part number and associated application information.

508-00118-32, 508-00118-34:

These 2 models are used on exciters with an output operating voltage range of 20 to 278 VDC. Theymount on 6A6 style exciters (with the smaller diode wheel). The 34 Detector incorporates a specialharness for mounting to diode wheels which do not have the harness groove (also the smaller 6A6 style

diode wheels).

508-00118-31:

This model is used on exciters with an output operating voltage range of 32 to 390 VDC. They mounton 7A6 style exciters utilizing the smaller diameter diode wheel.

508-00118-33:This model is used on exciters with an output operating voltage range of 60 to 525 VDC. They mounton 7A7 and 9A4 style exciters utilizing the larger diameter diode wheel.

1.3.2. Input Connections

The Detector receives input signals from the AC and DC terminals of the diode bridge via the wireharnesses (one on each side of the Detector). Each wire harness contains 3 pairs of leads for connection toeach pair of diodes. One lead of the pair connects to AC heatsink and other lead (DC lead) is routedthrough the diode wheel opening for that heatsink and connects to the DC buss. The A and C leads areencased in a harness and are routed in a groove in the diode wheel rim on the inboard side of the diodewheel (figures 3, 4, and 6). The length of the leads in the harness are sized to assure connection leadlengths match the mechanical arrangement of the correct AC phase. The leads must be connected to the

proper phase to avoid noise pickup from magnetic fields from the diode currents. The wires of theharnesses are routed through the diode wheel openings as shown in Figure 2.

The DC leads are connected to the DC buss ring as shown in Figure 3 and 5.

The AC leads of the Detector are connected to the AC heatsink assembly under one of the bolts securing theU shaped AC connection leads to the heatsinks. AC lead connection locations are shown in figures 3, 4,11 and 12. For lead assembly and torque of the bolts for U connectors refer to the brushless exciter instruction book.


8/29

POSITIVE POLARITY HARNESS

A AC

C DC

B DC

A DC

B+ A+C+ A-C-B-

NEGATIVE POLARITY HARNESS

DIODE FAULT MONITOR

DIODE WHEEL HUB

LAYOUT OF TOP VIEW OF DIODE WHEEL (RIM NOT SHOWN)

ARMATURE PHASE CONNECTIONS, C+, A+, B+ ARMATURE PHASE CONNECTIONS, B-, C-, A-

DC BUS RING DC BUS RING

AC HEATSINK

C AC

B ACO

Y

BL

BW R

G G O

Y

BL

W

WIRE COLOR CODEOGBL

ORANGEGREENBLUE

YRW

YELLOWREDWHITE

B BLACK

Figure 2: Block Diagram Of Detector AC And DC Connections On Diode Wheel

1.3.3. Output Connections

Two leads from the Ground Detector Transmitter (red and green) are routed to the Diode Fault Detector along the outboard face of exciter AC connection ring (see Figure 1) or in a groove at the ID of the diodewheel rim. These leads are connected to the DFD output terminals as shown in detail B of Figures 3, 4,11 and 12. After the leads are connected to the Detector, they are secured to the U connector near theDetector with glass cord and air dry varnish (Figure 1). The leads are then routed along the connectionring face (in nearly all cases these leads will be pre-routed).


9/29


10/29


11/29


12/29

1.3.4. Installation Instructions

Installation of these models is basically the same in that they all mount under the rim of the diode wheel(see Figure 1). They are also similar in that they contain a harness that distributes around the wheel andconnects across the series redundant diode assemblies located between the spokes of the wheel.At the time of this publication there were 4 models of Diode Fault Detectors as listed in section 1.3.1.

Normally these Detectors will be mounted on the diode wheels at the factory. However, if fieldinstallation is required the following sections will provide the instructions necessary for successfulinstallation or replacement of the Detector. Removal of the Detector which exists on the diode wheel isas simple as disconnecting all of the leads connected to the potted Diode Fault Detector module andremoving the module along with the wire harness (which is potted right into the module).

NOTE: Care should be taken when removing the RED and GREEN wires from the DFD. These

wires will remain and be re-used and must not be damaged (these wires connect the DFD

to the Ground Detector System and are difficult to replace if damaged).

Refer to section 1.3.4.1. for installation instructions on the 508-00118-31 and 32 Detectors. Refer tosection 1.3.4.2. for installation instructions on the 508-00118-33 Detectors.

Tools Required:v 3/8 torque wrench (small head is best) and 7/16 short socketv 1/4 small open end or combination wrenchv screwdriver (medium flat tip for #8 screw)v wire harness installation tool (provided along with the DFD)v Loctite 242 or equivalent threadlocker v Wire cutter, stripper, and crimping tools for 22AWG wire lugs

v Wire lugs (provided with the DFD)v allen wrench to fit 1/4 x 20 socket head boltsv nylon installation tools (provided with DFD for harness installation of 31 and 32 Detectors)

Kato Engineering part numbers: 172-60000-17172-60000-18


13/29

C

B

A

CONNECTIONLEADS

DIODE WHEEL ASM.

DIODE WHEEL ASM.

#1/4-20x1.5 MOUNTING SCREWS (2)FLAT WASHER, LOCK WASHER

ASSURE MONITOR IS SEATED AGAINT RIM I.D.

DIODE FAULT MONITOR

FACE VIEW SIDE VIEW

DIODE FAULTMONITOR

DIODE WHEEL RIM

OUTPUT TERMINAL ( + )

OUTPUT TERMINAL ( - )

LEADS FROM GROUNDDETECTOR TRANSMITTER

RED

GREEN

DC BUS

TERM./SCREW

FAN

RING

MODULE

LEADS TO AC/DC HEAT-

GROOVE IN DIODE WHEEL RIM ID

SINKS

DC

DCAC

DCAC

SLIDE HARNESS INTO GROOVEUNDERNEATH SLOT INSULATIONMAY NEED TO LOOSEN AC CONNECTORS

SIDE VIEW OF RIM NEAR AC HEAT SINK

HEAT SINK AC

AC HEAT SINKINSULATION

AC

Figure 6: Diode Fault Detector Outline of Mounting and Connections

1.3.4.1. 508-00118-31, -32 Style Detectors

Installation of these Detectors requires: installation of the wire harness, connection of the leads fromthe Ground Detection System (GDS) to the DFD output terminals, mounting of the DFD module, andtermination of the sensing leads encased in the wire harness.

** Wire Harness Installation:Installation of the wire harness on this type of DFD requires the wire harness to be wedged into agroove located on the ID of the diode wheel. Installation of this wire harness is facilitated through theuse of the nylon installation tools provided in the package along with the DFD. The tools and their associated Kato part numbers are listed in the above section under the heading Tools Required.To install the harness, first locate the DFD module on the spoke face of the diode wheel rim in whichthe module will ultimately be secured. Second, using the heavier of the two installation tools, push thewire harness into the groove between the diode wheel rim and the insulation papers found under theseries diode assembly heatsinks (figures 7 and 10 show proper installation of the wire harness). Careshould be taken when pushing the wire harness into the groove so as not to damage the sensing

wires. The portion of the harness nearest to the DFD module fits quite snugly in the groove.

Therefore, it may be necessary to loosen the AC link nearest to the module in order to get the

harness into the groove without damaging the sensing leads.


14/29

Spread the harness out around the diode wheel rim as it is being installed (the lead wires will beterminated during a later step in this installation process). Do not trim any sensing leads at thistime. The finer of the installation tools can be used to finish off the complete installation of the wireharness (press the harness totally within the groove). Make sure that the wire harness is totalencased by the groove in the rim the harness should not hang out beyond the edge of the rim

at any point.

** Connecting the Output Leads of the DFD to the GDS:

The next step is to connect the red and green leads which run between the GDS and the DFD. It iseasiest to connect these wires before final mounting of the DFD module is completed. To accomplishthis simply connect the ring lugged red wire to the terminal of the DFD which is closest to the diodewheel ID ( the red wire must be landed on the terminal closest to the edge of the diode wheel rim

the terminal furthest out on the radius ). Next land the lugged green wire on the other terminal of the DFD module ( the terminal closest to theshaft ).The lugs should be installed (if at all possible) with the barrels (crimped portion of the lug) pointing

out radially from the terminals (so that the centrifugal force will not turn the lug and terminal). Referto Figure 8 showing these terminations.

Care should be exercised when terminating or landing these leads so that they will not be

damaged or broken these wires are 24AWG stranded wire and can be fragile if mishandled.

Once these leads are terminated the terminals should be secured with a threadlocker (loctite 242 or equivalent) and sprayed with an air dry varnish.

** Mounting the DFD Module:

At this point the DFD module can be fastened to the diode wheel. The module is secured by (2) -20 x 1 socket head cap screws with flat washers. The screw should be secured with loctite 242threadlocker or equivalent and torqued to 50 in-lbs. While tightening make sure that the module is

seated tightly against the ID of the diode wheel (slightly pry the module up by inserting a flat tippedscrewdriver between the module and the shaft collar).Figures 7 and 8 show the installed module as it is mounted to the diode wheel.

** Terminating the Sensing Lead Wires:

Termination of the sensing lead wires is critical. This operation should be done carefully as the

lead wires are exposed to the full electrical and mechanical stresses produced by this rotary

excitation system.

Please refer to figures 3, 4, 5, 7, 9, and 10 for assistance in determining where and how each sensinglead should be terminated (if replacing a DFD module carefully examine and document the existinglead termination arrangement). Termination of these lead wires requires trimming each perspectivelead to the proper length ( very critical ), stripping back the Teflon coated wire, lugging the lead withthe proper type lug (these lugs are shipped in the same package that contains the DFD), and finallyterminating the perspective lead to the proper termination point. Within the package that contains theDFD module there are 3 different sizes of wire lugs. The smallest ring lugs (number 6 hole) are usedfor termination of the leads which connect the DFD to the GDS (this process should already have beendone in previous steps). Also included in this package are ring lugs containing a number 8 size hole(to be used to terminate the leads to the DC buss bar located on the outboard side of the diode wheel see figure 5). The remaining wire lugs in this package are the lugs that will be used to terminate thesensing leads to the AC connection links. These ring lugs contain a hole for securing the lead


15/29

directly to the bolts that fasten the AC connection links to the heat sinks of the series redundant diodeassemblies refer to figures 4, 7, and 10.

Termination of the sensing leads is best performed by starting at the DFD module (terminate thesensing leads closest to the module first then continue around the rim until all leads have been

properly terminated).

The diode wheel rim is the securing surface for all of these sensing leads. When terminating

these leads be sure that when the lead is finally landed in the correct location there is no

possibility for the lead to creep out or extend out in any way beyond the edge of the diode

wheel rim. The diode wheel rim protects the sensing leads from the centrifugal forces

present when the exciter is rotating.

Begin by extending the green wire down below the insulating paper and over the closest AC link mounting bolt. There is a green sensing wire that extends out from either side of the DFDmodule. Refer to Figure 4 to see how these leads are to be connected (the sensing lead wire color

is shown on this figure). Figure 4 does not show the AC connection links. However, the sensingleads are to be connected under the bolt head and on top of the connection link.Trim the lead wire so that after the lug is applied, and fastened to the proper connection link, thelead wire length is not so long that it may creep out from under the diode wheel rim when the unitis running. It is absolutely necessary that the sensing lead wire does not extend, or have thepotential to extend, out beyond the edge of the diode wheel rim once it is finally terminated

on the AC link. Figure 10 is a photo showing how these wires should look once terminated (this photo was taken without the AC link in place and was intended to show proper lead length andhow the sensing leads break out of the wire harness only).

The next step is to feed the red and black sensing leads through the diode wheel spoke openings

(windows). They should be fed through the windows in the locations shown on Figure 4. Thesensing leads are shown on this figure and are the red, black, white and yellow leads. After feeding the leads through the windows, measure and trim the leads. Then feed them back thoughthe window and strip and lug the lead wire. Feed the lugged wire through the window again as

before and terminate the lead on the DC buss in the proper location (use loctite 242 or equivalentfor securing the #8 screws used to terminate the leads which connect to the DC buss bars). Figure5 shows how they are to be terminated on the DC buss bars located on the diode wheel rimoutboard side (included in this figure is the color of the sensing lead as well as the proper locationfor termination to the DC buss). As before, these leads must be terminated short enough so thatthe potential for these leads to extend out beyond the edge of the diode wheel rim is non-existent.Make sure that the barrels of the lugs lay against the diode wheel rim. This will reduce the

chance of the lug turning under normal centrifugal loads.Figure 9 is a photo showing termination of a sensing lead to the DC buss bar. In this photo one of the yellow leads of the DFD is shown terminated along with the black lead from the GDStransmitter.


16/29

** Final Preparation:

Once all of the sensing leads have been properly terminated, the next step is to spray all of

the connection points with an air dry varnish.

At this point the installation of the 508-00118-31 and 508-00118-32 Diode Fault Detectors iscomplete.

Figure 7: Diode Fault Detector Mounting Face View (Photo)


17/29

Figure 8: Diode Fault Detector Top View and Output Connections to Ground Detector (Photo)

Figure 9: Diode Fault Detector Connection Example to DC Buss(Photo of 6A6 and 7A6 type exciter designs)


18/29

Figure 10: Diode Fault Detector AC Connection Example and Wire Harness Securing in DiodeWheel Groove (Photo of 6A6 and 7A6 type exciter designs)

1.3.4.2. 508-00118-33 Style Detectors

Installation of this Detector requires: installation of the wire harness, connection of the leads from theGround Detection System (GDS) to the DFD output terminals, mounting of the DFD module, and

termination of the sensing leads encased in the wire harness. If this is a replacement of an existingDFD module then carefully examine and document the installation as it exists. Also, the grooveshould be cleaned out thoroughly with a solvent. Cleaning of the groove is required so that the siliconsealant used to retain the harness will adhere properly to the coating in the groove.

** Wire Harness Installation:

Installation of the wire harness on this type of DFD requires the wire harness to be laid into a groovelocated on the ID of the diode wheel. The harness must also be installed in the groove underneath theseries redundant diode assemblies (the harness must be fed between the mounting block of thisassembly and into the groove in some cases loosening of the diode assembly may facilitateinstallation of the harness in this location). Centrifugal force exerted on this wire harness while theexciter is rotating is what will keep it in place.Spread the harness out around the diode wheel rim as it is being installed (the lead wires will beterminated during a later step in this installation process). Do not trim any sensing leads at thistime.

Once the harness is laid into the groove, apply 100% clear silicon sealant over the harness and into thegroove, at approximately 4 inch intervals around the diode wheel rim. Apply the silicon sealant sothat there is a bead of sealant approximately in length which fully fills the groove and encases theharness in that location. Make sure that the wire harness is total encased by the groove in the rim

the harness should not hang out beyond the edge of the rim at any point.


19/29

Allow the silicon sealant to skin and dry for about at least an hour before proceeding on with theinstallation process.

** Connecting the Output Leads of the DFD to the GDS:

Once the silicon sealant has dried sufficiently to hold the harness in place, the next step is to connectthe red and green leads which run between the GDS and the DFD. It is easiest to connect these wires

before final mounting of the DFD module is completed. To accomplish this simply connect the ringlugged red wire to the terminal of the DFD which is closest to the diode wheel ID ( the red wire mustbe landed on the terminal closest to the edge of the diode wheel rim the terminal furthest out

on the radius ). Next land the lugged green wire on the other terminal of the DFD module ( the terminal closest to theshaft ).The lugs should be installed (if at all possible) with the barrels (crimped portion of the lug) pointingout radially from the terminals (so that the centrifugal force will not turn the lug and terminal). Referto Figure 8 showing these terminations.

Care should be exercised when terminating or landing these leads so that they are not damaged

or broken these wires are 24AWG stranded wire and can be fragile if mishandled.Once these leads are terminated the terminals should be secured with a threadlocker (loctite 242 or equivalent) and the terminals sprayed with an air dry varnish.

** Mounting the DFD Module:

At this point the DFD module can be fastened to the diode wheel. The module is secured by (2) x20 x 1 socket head cap screws with flat washers. The screw should be secured with loctite 242threadlocker or equivalent and torqued to 50 in-lbs. While tightening make sure that the module isseated tightly against the ID of the diode wheel (slightly pry the module up by inserting a flat tippedscrewdriver between the module and the shaft collar).Figures 7 and 8 show an installed module as it is mounted to the 6A6 and 7A6 style diode

wheels. The mounting on this larger style diode wheel looks the same except that the rim isdeeper and the module nestles deeper into the rim (the entire DFD back radius fits under the

rim Figure 1 shows this).

** Terminating the Sensing Lead Wires:

Termination of the sensing lead wires is critical . This operation should be done carefully as thelead wires are exposed to the full electrical and mechanical stresses produced by this rotary excitationsystem.Please refer to figures 12 and 13 for assistance in determining where and how each sensing leadshould be terminated (if replacing a DFD module carefully examine and document the existing leadtermination arrangement). Termination of these lead wires requires trimming each perspective lead tothe proper length ( very critical ), stripping back the Teflon coated wire, lugging the lead with the

proper type lug (these lugs are shipped in the same package that contains the DFD), and finallyterminating the perspective lead to the proper termination point. Within the package that contains theDFD module there are 2 different sizes of wire lugs. The smallest ring lugs (number 6 hole) are usedfor termination of the leads which connect the DFD to the GDS (this process should already have beendone in previous steps). Also included in this package are ring lugs containing a number 8 size holewhich will be used to terminate the sensing leads contained within the wire harness to the AC and DCsides of the series redundant diode heatsinks.


20/29

The AC sensing leads will all connect on the inboard side of the diode wheel assembly. Figure 11displays the complete diode wheel assembly and Figure 12 shows, in greater detail, the inboard side of the diode wheel assembly.

Termination of the sensing leads is best performed by starting at the DFD module (terminate thesensing leads closest to the module first then continue around the rim until all leads have been

properly terminated).

The diode wheel rim is the securing surface for all of these sensing leads. When terminating

these leads be sure that when the lead is finally landed in the correct location there is no

possibility for the lead to creep out or extend out in any way beyond the edge of the diode

wheel rim. The diode wheel rim protects the sensing leads from the centrifugal forces

present when the exciter is rotating.

Begin by extending the green wire from the wire harness and out to the first heatsink. There is agreen sensing wire that extends out from either side of the DFD module. Refer to Figure 12 to see

how these leads are to be connected (the sensing lead wire color is shown on this figure). Trimand lug the wire such that when landed the wire will lay on the rim of the diode wheel and not betoo loose to hang out beyond the edge of the diode wheel rim.It is absolutely necessary that the sensing lead wire does not extend, or have the potential to

extend, out beyond the edge of the diode wheel rim once it is finally terminated on the AC

link. Next apply loctite 242 or equivalent threadlocker to the #8 screw which will be used to secure thesensing lead to the heatsink and terminate the lead to the heatsink.

The next step is to feed the red and black sensing leads through the diode wheel spoke openings(windows). They should be fed through the windows in the locations shown on Figure 12 (these

are the red, black, yellow and white wires). After feeding the leads through the windows, measureand trim the leads. Then feed them back though the window and strip and lug the lead wire. Feedthe lugged wire through the window again as before and terminate the lead on the DC buss spidersin the proper location as shown on Figure 13 (again use the loctite 242 or equivalent). As before,these leads must be terminated short enough so that the potential for these leads to extend out

beyond the edge of the diode wheel rim is non-existent. Make sure that the barrels of the lugshang radially outward from the heatsinks. This will reduce the chance of the lug turning

under normal centrifugal loads.

Continue around the rim terminating each sensing wire as shown on figures 12 and 13 using thesame procedure as outlined above.

** Final Preparation:

Once all of the sensing leads have been properly terminated, the next step is to spray all of

the connection points with an air dry varnish.

At this point the installation of the 508-00118-33 Diode Fault Detector is complete.


21/29

F I G( 7 A


22/29

FIG(7A


23/29

FI(7


24/29

1.4 Description of Operation

1.4.1. Diode Fault Detector Circuit Overview

The Diode Fault Detector senses the forward voltage drop of the series redundant diodes within the rectifier bridge. Normally the forward voltage drop of each diode is about .7 and 1.2 volts DC or 1.4 to 2.4 volts for bothdiodes. When one of the diodes fail either shorted (predominant mode) or open, the forward drop changessignificantly with respect to the other legs. The Detector senses this change by monitoring the filtered ACcomponent of the composite forward voltage drop signal of all the legs of a given polarity. Referring to block diagram of the Detector (Figure 14), the following describes the basic circuit elements of the Diode FaultDetector:

1. The Detector senses the forward voltage drop of the diodes in positive and negative buss separately. For each polarity, the Detector receives the signals from the 3 AC phase connections and the DC output buss(positive or negative). These signals are fed into a high or low value gate (A0) to detect the largest absolutevalue of the potential difference as referenced to the DC buss. This is the unfiltered composite forwardvoltage drop.

2. The output of A0 is then limited by the clamping circuit A1, filtered by circuit A2 (band limiting ) , and low

pass filtered by A3 to attenuate high frequency noise and bridge harmonics.3. The filtered signal is fed into a high pass filter A4 to obtain the AC coupled ripple voltage or AC componentof the filtered forward voltage drop signal produced by the bridge.

4. The AC component of the filtered forward voltage drop signal from item 3 is converted to a DC signal by precision rectifier A5. Circuit A6 is a pure integrating amplifier which provides added noise immunity andfault detection delay timing to the AC ripple signal.

5. The resulting AC ripple signal is compared to a preset thresh-hold voltage for alarm, Vref1 or Vref2. Whensignal exceeds the thresh-hold, output of the comparator A7 goes low signaling a diode fault condition.

6. The diode fault signals from the high and low side Detector circuits are passed to a low value gate (LVG), A9along with a square wave pulse of about 1 to 2 Hz. With a normal condition, the diode fault signals are highand the LVG , A9 provides a square wave output signaling a normal condition. If either of the diode faultsignals go low, the square wave signal is inhibited and the LVG output stays low indicating a diode fault hasoccurred.

7. Circuit A10 monitors the input DC voltage and provides an inhibit signal when the input voltage is below the preset threshold (about 32 Vdc for a 31 Detector). When the input DC voltage rises above the threshold ,A10 goes from high to low (no inhibit). This signal is fed into the high value gate (HVG) A11 along with thediode fault signal from A9 and it serves as to inhibit the diode fault signal from A9 when high. This preventsspurious or unpredictable Detector operation when the exciter is operating at low voltage.

The preset threshold for: 508-00118-32, 34 is approx. 20VDC508-00118-31 is approx. 32VDC508-00118-33 is approx. 60VDC

This is the level of main field excitation at which the Diode Fault Detector will begin to monitor the status of the diode wheel and series redundant diodes. It is at this point that the Detector will begin to output a signal(pulse or continuous output).

8. HVG, A11 provides the diode fault alarm signal to an external device such is the optical isolator of theground detector transmitter. The opto-isolator is connected between Detector DC+ and the output of A11,thus when A11 is low, the current flows (1 to 2 ma) through the isolator driving it to a high state (diodefault). The transmitter sends this signal to the receiver which causes the diode fault alarm to go high, 24 Vdc.

When the output current of A11 is 1 to 2 Hz square wave, this indicates a normal condition. The resultingsignal out of the ground detector receiver is a 1 to 2 Hz square wave , 0 to 24 Vdc.

When the diode fault signal at A11 is high, current output to the transmitter is zero. This indicates anundervoltage condition (from A10) or malfunction condition (under most conditions the current output will


25/29

go to zero when a malfunction has occurred). The diode fault signal output from the receiver will beconstant at about 0 Vdc.

9. Thus, the Diode Fault Detector alarm signal has three states which allows the indication of normal, alarm, or malfunction / undervoltage condition. These states are summarized in Figure 15. The receiver sends thediode fault alarm signal along with the generator ground fault alarm signals (see separate instruction book) toa remote device for indication to user.

GEN.FIELD

DIODE

DIODE BRIDGE ASM.

+

-

AC VOLTS ARMATURE

HVG AC TODC CNV.

LIMITER/FILTERS

Ks + m

VREF1

AC TODC CNV.

LIMITER/FILTERS

Ks + m

VREF2

HIGH SIDEPOWER SUPPLY

LOW SIDEPOWER SUPPLY

LVG

COMPARE

COMPARE

UNDER VOLTAGELOCKOUT

DIODEFAULTSIGNAL

DC +

DC -

RED

GREEN

FIELD GROUND DETECTOR TRANSMITTER

DIODE FAULT SIG.

DIODE FAULT MONITOR

FIELD GROUND DETECTOR RECEIVER ( STATIONARY)

HVGOUTPUT

TELEMETRY CIR.

GROUND FAULT DET.CIRCUIT

TELEMETRY CIR.

FIELD GROUND ALARM0 TO 24 VDC OUTPUT SIGNALS

FIELD GROUND DETECTOR MALFUNCTIONDIODE FAULT ALARM.

INPUT POWER (24 VDC)

PICK-UP COILS

OPT. ISO.

ROTATING COMPONENTS

EXCITER

A0 A1 A6 A5

A2-A4

A7

A8 A9

A10

A11

A0

A1

A6 A5 A2-A4

A7

1 - 2 HZ SQUARE WAVE

NORMAL SIGNAL

+-

+-

Low Side Monitoring Circuit

High Side Monitoring Circuit

DC +

ISO. AMP/

LVGISO. AMP/

FIGURE 14: BLOCK DIAGRAM OF DIODE FAULT DETECTOR /FIELD GROUND DETECTOR


26/29

1.4.2 Diode Fault Detector Output Signals

The Diode Fault Detector is used in conjunction with brushless exciters with series redundant diode bridgearrangement and the field ground detector (see separate instruction books). The Diode Fault Detector outputsignals as transmitted via the Ground Detector System are shown below.

Normal Signal No Alarm

1 to 2 Hz Frequency

Diode FaultAlarm Signal

Recommended Time Delay to Alarm - 20 Sec to Alarm.Set to Alarm on less than 4 pulses (.15 sec Min.Pulse width) in Rolling 20 second Period

Diode Detector Undervoltage/MalfunctionAlarm

Figure 15: Diode Fault Detector Alarm Logic

2. INITIAL INSPECTION, STORAGE AND ALIGNMENT

2.1. RECEIVING INSPECTION

The Diode Fault Detector comes mounted and pre-wired to the diode wheel of the brushless exciter which iscarefully crated for shipment and can withstand most shocks incurred during transit. Before accepting shipmentfrom the transportation company, examine the crating carefully per exciter instruction book. If the Diode FaultDetector is shipped as a separate or replacement part unpack and check for damage to the module or wires.

Notify the transportation company claims office and Kato Engineering if damage is found. Be sure to givecomplete and accurate details when reporting damage.

2.2. ALIGNMENT AND ADJUSTMENTS

The Diode Fault Detector does not require adjustment or alignment. Some brushless exciter disassembly isrequired to access the Diode Fault Detector and ground detector. Remove the exciter end cover, grounddetector mounting cover , exciter fan, and fan baffle per the exciter instruction book. The Diode Fault Detector will be accessible through the ground detector cover opening and from the back of the exciter (monitor leads).Mount the Diode Fault Detector to diode wheel per paragraph 1.3. Be sure to use a thread lock adhesive on allthe threaded fasteners of the Detector. Lock exciter fasteners per the exciter instruction book.

24 V

0 V

24 V

0 V

24 V

0 V


27/29

3. MAINTENANCE

3.1. PERIODIC MAINTENANCE

The Diode Fault Detector requires no maintenance beyond that required for the exciter to which it is mounted.Check connections for damage or upset during exciter maintenance. Any connections removed and replacedshould be sprayed with a good quality, air drying insulating varnish.

3.2. REPLACEMENT

If replacement Diode Fault Detector is required refer to section 1.3 for assembly/disassembly.

3.3. INSULATION RESISTANCE

Periodic measurement of the insulation resistance may prevent a serious problem caused by a double ground.Readings with a 500 volt megger of the combined exciter rotor, diode wheel, Diode Fault Detector, and generator

field may be made. Refer to the exciter instruction book for further information.


28/29

3. TROUBLESHOOTING

4.1. Diode Fault Alarm

If a diode fault alarm occurs, the redundant diode will, under normal circumstances, continue to providerectification for the leg. The diode may be visually inspected during operation using a strobe light through anaccess plate on the end of the exciter to see if there is mechanical damage.If the exciter continues to function normally, the rectifier assembly may be checked at the next planned outage.The diodes can then be checked per the exciter instruction book.If no diodes are found to be faulty. Disconnect the Diode Fault Detector wires and check per paragraph thefollowing few paragraphs (sections 4.2., 4.3., 4.4., and 4.5.).

Note: If both diodes fail in the same leg then excitation will be lost.

4.2. Troubleshooting General Method

A digital voltmeter with diode check scale, 0 to 50 VDC power supply, and a function generator are useful in

locating problems with the Diode Fault Detector.

4.3. Wire Continuity Test

Disconnect the AC and DC input leads of the Detector and the ground detector output leads. With a digitalmultimeter (similar to an 8060 Fluke digital meter) with diode check feature, check the continuity between the ACand DC leads to determine if there are any wire breaks. The readings will range from 10K ohms to 5 Megohmand some leads will be polarity sensitive. The magnitude of the reading not important, just determine if any wirehas broken. Check the continuity of the red and green diode wires from the ground detector.

4.4. Checkout of Signal Wires to Ground Detector

Align the ground detector pickup coils. Then apply about 2 mA across the red (plus) and green (minus) lead. It isrecommended that a limiting resister be placed in the circuit to protect from over current. The current must notexceed 25 mA. With 1 to 2 mA current, the diode fault signal out of the receiver assembly should go high (about24 VDC). The output signal should go to zero with no current. If it does not respond as described, the grounddetector transmitter circuit is faulty and the transmitter should be replaced.

4.5. Functional Check of Diode Fault Detector

Reconnect the ground detector red and green wires to the Detector. Alternately, the Diode Fault Detector output

terminals may be connected to an ammeter (0 to 10 mA scale). The Diode Fault Detector can be functionallychecked using a variable power supply 0 to 50 VDC (floating / ungrounded). Connect power supply to the DC buss leads, leave the AC leads connected. A 1 to 2 Hz square wave output current should appear at DFD outputterminals at about 32 VDC on 31 DFDs (20VDC on 32 and 34 DFDs, and approx. 65VDC on 33 DFDs).Then connect a function generator set for 250 to 400 Hz square or sine wave, 0 to 5V to between one of the ACleads and the corresponding DC signal lead (this AC lead will have to be disconnected from the exciter AC linksand heatsinks). The function generator is being used here to simulate an AC ripple on the forward voltage dropthus simulating a failed diode. Measure the function generator output with a digital voltmeter on RMS scale.Gradually increase the function generator voltage. At about .5 to 1 Vrms, the Diode Fault Detector output or alarm signal current should change from a square wave signal to a steady 1 to 2 ma signal. Check the other AC


29/29

leads in the same manner. If the Detector checks good , contact GE representative for assistance. If the Detector checks bad, replace with a new one. There are no serviceable parts.

4.6. Replacement Part Numbers

GE Part Number Kato Engineering Part Number Operating Range351A6424P0001 508-00118-31 32 to 390 VDC351A6424P0002 508-00118-34 20 to 278 VDC351A6424P0003 508-00118-32 20 to 278 VDC351A6424P0004 508-00118-33 60 to 525 VDC

diode fault detector

Documents