THE STORY OF THE P&H MODEL 2800

By     Richard “Chubby” Czubkowski

1968-70  -- FIRST P&H MODEL 2800 with ELECTROTORQUE  MKI ------






Preliminaries ----


Starting in 1960, the shovel R&D groups along with Motor Engineering and production people were working on what was needed for the first big shovel. After much engineering discussion, concepts had to be turned into reality.  The new big shovel was named P&H Model 2800 MKI with
P&H ELECTROTORQUE CONTROL.


The P&H 2800 MKI were purchased by Kaiser Resources for coal mine in British Columbia, Canada. In fact they purchased four 2800s.


The 2800 was the largest crawler mounted, hard rock loading shovel, to be paired with 200 ton trucks. Beside the innovated control called ELECTROTORQUE MKI, there were many other innovations in mechanical, electrical and operational concepts;


START-UP OF THE FIRST 2800 MKI -----


The 2800 went to work at the Kaiser mine in 1969. There were many startup problems. New ideas were modified and some replaced with experienced ideas. With four machines in a row, field problems on the first machine had to be resolved quickly.  


Mechanically -----------------




Electrical ----------------------------


The system was designed with a single armature supply transformed with  multiple  secondaries.  

 

 From the 1900B experience it was found that di/dt was best relegated to the  convertor system. The new transformers were designed to have an overall low  impedance and equal impedance between the primary and each secondary.  Because the motions work together, VA, plus and minus, are being transferred  between the secondaries, and not replaced to the primary.   This had to be  considered in the VA rating of the windings.


The new coils are vacuum impregnated with vanish and over coated to give extra  protection to the moisture and dirt of the mining environment.  A Milwaukee  company,  Sorgel made the new transformer coils with copper wire conductors  and multiple  layers of Nomex for insulation.  All the existing transformers were  reworked and the  coils were placed on the same Urethane shock absorbers.


The items listed were just a few problems that were found after a few hours of operation.  Many of these new innovations were modified, reworked and improved by dedicated P&H Engineers and ASEA Engineering who knew that this type of machine was the future in large shovels.


In 1999, the score card reads as follows;

One 2800 MKI ------- 139,000 hours

Second 2800 MKI ----- 135,000 hours


Two other MKI shovels, of the original four machine order, were retired after 100,000 hours.

The original four 2800 had been upgraded, mechanically and electrically. The hours they had acuminated are a tribute to P&H Engineering and Service.

(See Summary)


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MODEL

CAPACITY

LOAD RATING

YEARS  MFG.

2800 MKI

24-16 CY.

60sT

1969-1975

MODEL

CAPACITY

LOAD RATING

YEARS  MFG.

2800 MKII

26-28 CY.

90sT

1975-1983

MODEL

CAPACITY

LOAD RATING

YEARS  MFG.

2800XP

28-32 CY.

110sT

1982

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1965 JOINT VENTURE AND THE EXPERIMENTAL 1900B -------------------


To expedite the development, a joint venture partner was investigated. AIG, BBC, Siemens and ASEA were approached. They were all involved with heavy duty application for railroading. ASEA of Sweden was chosen because of their heavy duty application on trains and they manufactured “big” Thyristors. In 1965 a joint venture was initiated.



1900B ----


Through the collaborative effort of ASEA and P&H Engineers, a system was designed. ASEA was responsible for the control/convertors and P&H was responsible for the application and the rest of the shovel system hardware.


A conventional  1900  was a  reworked with two hoist motors, field and Armature transformers, joy sticks, capacitor cabinets,  ventilation changes, F# motion motors etc..


The main ASEA cabinet consisted of a series of drawers or trays which contained the Thyristor modules, electronic power supplies, control relays, indicator tray for trouble lights and the motion controls. Because of the Thyristors capacity, several motions used Thyristors in parallel


Since the concept was new to mining and mine personnel, the thought was to replace drawers for ease of trouble correction.  The control system was labeled “Works in a drawer”. This would eventually prove to be a rather cumbersome concept. Some of the drawers were too heavy to lift by a single person.


The first Thyristors powered shovel went to work at the beginning of 1968, in the CCI iron mine in Republic Mich. It based on a Model 1900. The static shovel was named 1900B, 12CYcapacity. . The control system was called P&H ELECTROTORQUE.  The MKI was later added to distinguish it from the future designs.


Since it was new technology, it was a frustrating time and learning experience.  We had to learn fast because there were four Model 2800s, destined for Kaiser Resources in British Colombia Canada by the end of the year.  There was no knowledge or past history of this type of shovel application. We learned by field experience.


Many problems were encountered including soft pit power networks and outages. Transformer impedance was a problem. The secondary’s had unequal impedance to the primary. Between the impedance of the transformer and the impedance of the supply there are not enough short circuit to blow the fast acting, sliver sand fuses, to protect the thyristors.  


Countless of autopsies were performed on thyristors and fuses. It was evident that the short circuit current was not enough to blow the fuse rapidly and the thyristor suffered over current and failed. The thyristors fault, over voltage or current, could be determined by the size and location of the ruptured Silicon wafer and the degree of fuse link rupture. This was a learning experience for the P&H Engineers.


Tuned capacitor banks were added to the main transformer secondary’s for filtering and to improve the short circuit capacity for converter operation. This was a start of the RPC, Reactive Power Compensator, featured on all of P&H DC shovels.


The dynamic nature of the loads, produced by the motions, was a problem. The shared power supply between transfer from crowd and propel was a problem. Thyristor failure and fuse blowing were normal.

 

 Failure to have bridge reversing and applying braking power resulted in propel run away and re- winding of the hoist drum cables.   The list of problems was long but the experience would lead to the future success to the P&H Electrotouque. .


Through the efforts of two novice engineers, servicemen, an occasional engineer from ASEA, long hours, weekends and good the backing from Les Price, the 1900B survived in the CCI Iron mine. After being tortured by digging Taconite over burden, many changes and reworks, the shovel was sold and transferred to a mine in Arizona.   


The basic system proved to be workable. Dynamic motion improvements were apparent while digging and swinging.  The system would convert power to do work and invert power to the net when braking a motion. Power consumption was less but was not advertised because the KWH/ton was less as compared to the Magnatouque machines. Magnatouque shovels were P&H’s bread and butter.


The 1900B was the most powerful 12 CY shovel. It was the first shovel with static convertors powering DC motors.   It was a first for P&H and around the world.     

1975 ---- 2800MKII  with ELECTROTORQUE  MARK II ------






Mechanical improvements or modification were made based on the experiences from the 2800 MKI. Structure were improved or modified to accommodate the improved load rating.

Thyristors were improving in current capacity and voltage rating.


In 1973, a MKII version of ELECTROTORQUE was designed. The MKII consisted of a CONTROL CABINET and separate oil cooled CONVERTER CABINET designed by ASEA.  The Control Cabinet, Transfer Cabinet, Auxiliary Cabinet, and Operator Console etc., were P&H designed and manufactured.    


The Control Cabinet had individual rack mounted circuit cards (ASEA Combi-flex) for motion control, armature and field, and RPC control. This cabinet also contained the feedback circuits, power supplies, control relays, field converters and miscellaneous control parts.  An input jack was added to the meter panel so test voltages could be measured on the comb flex card.


The Convertor cabinet contained the motion armature Thyristors and the Thyristor/Thyristor RPC switches to control the steps of the tuned capacitor banks. All banks were tuned to approximately the 4.5 harmonic with air core reactors.

Static converters have an inherent poor line power factor when the motion motor is near stall. A stepped Reactive Power Compensation, RPC system, was applied to ELECTROTORQUE shovels to compensate for the inherent VARS.


 Since the hoist had two motors, they were connected in series. Two 3PH full wave, double way bridges were connected in series, controlled in booster or push-pull configuration. This reduces the inherent VARS produced by the converters at near stall.


The RPC Switches controlled the tuned banks of capacitors. All the banks were charged to the peak voltage by one of the back to back Thyristors. The system was able to reverse the DC charge periodically on the AC rated capacitors. When VAR correction was need, the RPC Switch would turn on at the peak of the line without disturbing the line voltage, to compensate for the negative VARS produced by a motion convertor. A VAR transducer and the RPC controller connected and disconnected the tuned banks of capacitors as correction was needed.  


The original MKII oil cooled converter had a series of over-coolers on top of the Thyristors pole face with the other pole face connected to a long under cooler. This under cooler also served as the AC bus for the various Thyristors bridges. To electrically isolate each Thyristors from the others, a ceramic Beryllium oxide wafer was placed between the top pole face and the over cooler. The individual convertor bridges were equipped with Current Transductors for current feedback


First MKII shovel -------------------


The first shovels were places at Kennecott Copper Mine in Bingham Canyon, Utah in 1975.This were the biggest loading shovel in the pit at 27 CY.


An immediate problem was misfiring of the converters at high current levels. The internal pulse transformer, of the pulse firing modules, was susceptible to miss-fire due to high electromagnetic fields.     A metal shield or box was put around the epoxy encapsulated firing modules.


A further problem developed with the firing modules with time. Several modules were x-rayed and engineering determined that the epoxy used, after thermal cycling, was flexible and small components, like diodes, were destroyed because they were fixed in place and could not move with the encapsulation.  The problem was solved by conformal coating the circuit boards for placement in the metal box.   


Because of the cost from ASEA, P&H Electrical Engineering took over the design of the convertor cabinet and improved their manufacturing and reliability. There was a potential health hazard involved with Beryllium wafers which insulated the pole of the thyristors from the over cooler. P&H Electrical Engineering designed an insulated bellow with an “O” ring seal, which isolated the over coolers and prevented leakage of the cooling oil.  Some convertor parts were supplied by ASEA; but the majority of the components were manufactured in-house or by local vendors.


P&H Electrical Engineering also made modification to the original ASEA supplied Combi-flex circuit cards.  A P&H company called Control Logic was given the manufacturing drawings of the card assemblies and produced Combi -flex boards. Later, Milwaukee Electronics took over the circuit card manufacturing.


Certain proprietary parts were purchased from ASEA and others bought on the open market. When components became hard to purchase, P&H Electrical Engineering designed new more readily available components. In 1976, P&H had taken over the design and manufacturing of the MKII system.


When the MKI components became unavailable, P&H Engineering designed retrofit control trays using Combi-flex cards and card racks.


RPC Capacitors ------


In 1976, the use of PCBs was being outlawed.  The insulating oil in the AC Power factor correction capacitors contained PCBs.   The Power Factor capacitors used were compact because of the use of the film-foil technique and insulating oil which constrained PCBs. Since PCBs had to be eliminated, GE approached P&H Engineering to participate in redesigns of the capacitors.  The writer participated and a new 600vac, Power Factor capacitors with mineral oil was put on the market. Since the P&H application was unique the insulation oil contained an additive to allow prolong DC to be applied to the units.  P&H also insisted that additional over voltage testing be done on each unit similar to utility test standards. The increase over voltage testing reduced the number of failed capacitor dramatically


Because of the new dielectric oil was flammable a pressure switch was added to the individual capacitor units to prevent rupture.  The film-foil capacitors have a tendency, over time, to develop minute shorts between the layers of foil. The shorts produce gas in the oil which over time can expand the capacitor can.  Eventually the can may rupture.  A pressure switch, inside the can, was connected to a control circuit which disconnected power from the capacitors.       


MSHA -----


The Federal MSHA regulations had clauses to protect motors and wiring. Motor had to have individual short circuit and overload protection. Wiring had to have branch circuit protection.  Hence, new shovels were fitted with auxiliary motor starters and load panels for branch circuit protection. The electrical system was refined and problems solved.


Improvements were made to suppression of over voltages and for surge protection from the incoming high voltage supply.  Improvements were made for reliability.


The thyristor cooling oil was flammable. With dust, poor maintenance and the extreme shock environment of shovel operation, a broken wire or short in the convertor wiring resulted in burning of the bellows, oil leaks and oil ignition. Wrapping the bellows with insulating tape, proper maintenance and fire suppression helped minimizing the problem.


K FRAME MOTORS     1976-77 ------------------------

The F motors were replaced by the K series motor.  The main difference was the elimination of the laminated field structure. The frame or field structure was a rolled heavy plate without the laminated inserts. The rest of the motor designed was mainly the same. The new K motors characteristic were ideal for shovel motion duty, exhibiting good thermal properties and transient commutation capabilities.


1981 ----- 2800XP  with  P&H ELECTROTORQUE -----------------






In 1981-82, the shovels with the XP, Extra Performance designator, were introduced.  


Features ----------------


The DIVERTOR System was self contained in the Converter cabinet. It consisted of a Hall current sensor on the DC output to the motion motors. Charged capacitors, at higher than the maximum DC output bus, were controlled by a Thyristors directly  connected to the DC bus. When a DC over current was sensed, a Thyristor applied  the capacitor voltage in the opposite direction of the DC output voltage. At the same  time the gating of the bridge’s Thyristors stopped. The voltage and current, stored in  the capacitors, commutated off the bridge current, preventing motor flashing and limiting the over current of the bridge Thyristors.  


 

An external DC supply was used to charge the capacitors to the peak of the AC  line. This resulted in a cost saving and simplified the control system. The AC  power capacitors had special additive in the dielectric to withstand the DC  voltage without deterioration


 

The main transformer underwent a change in vendor.  Sorgel had been bought by Squire D and moved the big transformer production out of Milwaukee. NECO who became NECO/Hammond or Hammond, a transformer manufacturer, was chosen to build the Mains (Armature transformers). P&H Engineering worked with NECO. The final configuration would be Copper sheet wound, multiple layer of Nomex insulation and a double vacuum impregnation to insure an outside coating of varnish to ward off the mining environment.  The sheet windings had to be configured or arranged to give the specified impedance parameters of this multi secondary transformer.


 The coil assembly was than sandwiched between thick insulating boards, placed on the laminated core leg and held in place by jack screws  to the core proper.  The urethane bumpers were eliminated. The overall design concept was to that the windings were locked in place by the winding technique and the varnish impregnation.


 A series of strategically placed duct sticks in the winding, held in place by the sheet winding and vacuum impregnation of the coil assembly allowed for good thermal conduction and thermal overloads.  The entire coil assembly was held rigidly in place by the jack screw and the entire unit. The coils and core, would like a solid assembly against the shock and vibration of the shovel.

 

 The design and manufacture had it startup problem. Modifications were made  mainly in the use of multiple layer of the layer insulation, assemble and quality  control. The improved winding technique and assemble proved to be reliable  both electrically and for longevity.



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