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FORMER GERMAN SUBMARINE TYPE IX-C |
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MOTORS AND CONTROLLERS |
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SUMMARY |
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| The German application of auxiliary motors and their associated controls is of rugged and simple design which requires increased responsibility on the part of ship's personnel for starting and operating his equipments. | |||||
| Simple compact manual controllers are used extensively for motors regardless of size. Magnetic controllers are seldom employed. | |||||
| The German motors are of the usual D.C. types normally found in U.S.N. Submarines, being compact and light in unit weights. | |||||
| A novel feature of motor design with regard to U.S.N. submarine practices past and present incorporates the use of a series starting field for minimizing inrush currents rather than external starting resistors and their associated accelerating relays as is present U.S.N. practice in submarines. | |||||
| External shock mounting in form of bonded rubber mounts both in compression and shear was used extensively | |||||
May, 1946 |
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PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H. |
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TABLE OF CONTENTS |
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9C-S63 |
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C O N F I D E N T I A L |
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AUXILIARY MOTORS AND CONTROLLERS |
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| A. Descriptive | ||
| (a) Introduction | ||
| The scope of this report is concerned primarily with the ideas and manner of application rather than a detailed discussion of the physical structures installed. Without reservation, the German structures at best are of no better design than corresponding present U.S.N. equipment. For detailed information regarding the individual circuit connections, reference should be made to the German Instruction Book, "Stromlauf und Auschlusspläne für die Hilfschalttafeln und Kraftstromverbraucher auf U Booten Typ IX C and IX D2" (Circuit and Connection Plans for Auxiliary Switchboards and Auxiliary Machinery for U-Boats Type IX C and IX D2). Assembly drawings of several types of motors and controllers including magnetic controllers are contained in German Instruction Book "Beschreibung und Betriebvorschrift für Elektrische Unlagen" (Description and Operating Instructions for Electrical System). | ||
| In addition, reference should be made to German Instruction Book "Grundzuge, für Electriche Unlagen - Berlin 1940" (Outline for Electrical Systems) in which a separate section is devoted to submarine installations. In it is outlined the necessary shipboard tests for auxiliary equipments including detailed tests required for motors. | ||
| A magnetic type steering controller has been sent to BuShips, Code 660 for detailed study and reference should be made to the Bureau's report when it has been written. | ||
| (b) Description | ||
| I. Controllers | ||
| A study of German motor and controller application leads one to observe the following basic difference between his concept and present U.S.N. practice. In the extensive use of simple manual controllers, the German places considerably increased reliance on his operating personnel to start and operate his motors and at the same time, due to the simplicity of his installations, requires | ||
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| considerably less skilled electrician's mates to maintain them. In addition, his units take up less space and weigh less than U.S.N. units. When integrated over the vessel as a whole, weight and space reductions are of considerable magnitude. To amplify these statements, a comparison of controllers for High Pressure Air Compressor Motors is presented. | |||||||||||||||||||||||||||||||||||||||||
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| In the few cases where magnetic controllers are used, they are of much smaller size and simpler design than present U.S.N. practice. This is due primarily to the German replacement of starting resistances with series starting windings in the motor. The operation of the magnetic controller will be more fully discussed further along in the report. At this time it is desired to show the space and weight relationship between the German magnetic controllers and present U.S.N. units; for this purpose, a comparison between the German magnetic controller for the Hydraulic Pump Motor and the corresponding U.S.N. controller is presented. | |||||||||||||||||||||||||||||||||||||||||
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| Inspections of controller structures revealed that: | |||||||||||||||||||||||||||||||||||||||||
| (1) Standard methods of manufacture have been employed, special tooling to manufacture parts being kept to a bare minimum, with an emphasis on designs that might readily be manufactured in any shop. | |||||||||||||||||||||||||||||||||||||||||
| (2) The final assembly is composed of several well grouped subassemblies. | |||||||||||||||||||||||||||||||||||||||||
| (3) In general, the housings are made of simple sheet metal structures, with varying degrees of drip-proof effectiveness, attained primarily by proper shaping of the sheet metal. Watertight or pressure-proof controllers do not appear to have been used nor was their use anticipated in plans available. | |||||||||||||||||||||||||||||||||||||||||
| (4) The units are designed for maximum accessibility for maintenance and renewal of parts; however, this feature has been frequently lost when installed in the vessel due to the location with respect to other installed equipments. | |||||||||||||||||||||||||||||||||||||||||
| (5) Captive screws are used extensively and various methods are incorporated in the components to minimize the possibility of incorrect reassembly when taken apart for maintenance. | |||||||||||||||||||||||||||||||||||||||||
| (6) In many cases, contacts have been designed to be reversible. By removing two securing screws, the damages contact surface may be turned over, secured, and put in service without recourse to a spare parts box. | |||||||||||||||||||||||||||||||||||||||||
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| (7) Bolted patch plates are used extensively on which the necessary tube terminals were secured. The plate can be removed, sent to the shop, while the controller is being installed. This feature resulted in a saving of installation time at the shipyard in that the controller does not have to be disassembled to install the tube terminals in the controller housing as is frequently the case in U.S.N. controllers. In some cases it appears the German has assembled the tube terminals at place of manufacture. | ||
| (8) The manual controllers are provided with a star wheel spring loaded actuating mechanism, and a return spring. Holding coils are provided to minimize the possibility of opening the circuit under shock conditions. These coils also serve as blowout coils. In addition, nearly all controllers are provided with low voltage protective devices (relays) which short out the holding coil when the protective device drops out. They are usually set to drop out at 75 volts. The controllers must be manually reset if tripped due to low voltage. The circuit fuses provide the only overload protection for the equipment. | ||
| (9) The controllers are usually inserted in only one leg of the circuit between the supply switch and the motor. No attempt is made to designate one leg as being more desirable than the other, as either one has been used. In some cases on smaller motors, the controller serves as a disconnect switch as well, both legs of the circuit being broken in those applications. | ||
| (10) In several cases, particularly controllers for motor generator sets, the units are designed to operate from either 110-170 volts or from 220-340 volts by making the desired external connections. A built-in dropping resistor reduces the 220-340 volts to 110-170 volts. | ||
| (11) Louvers and "hat" type ventilators were used to increase natural ventilation in the various controllers. | ||
| An example of the operation of German manual and magnetic controllers is presented for record purposes. | ||
| a. Manual Controller for High Pressure Air Compressor Motor: | ||
| The electric air compressor motor is the largest auxiliary motor installed (approximately 82 H.P.) This motor is provided with a series connected starting winding as the only means of limiting the inrush currents. The controller is provided | ||
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| with seven positions including an "off" position. Between positions 1 and 5 inclusive the electrical connection is not changed in any manner. The additional steps providing a mechanical time lag before the motor is connected across the line, thus minimizing the possibility of insufficient acceleration before placing the motor across the line. It is finally connected as an adjustable speed shunt motor. | ||
| b. Magnetic Controller and Selector Switch Installation for Main and Standby Hydraulic Pump Motors. | ||
| There are two hydraulic pump motors controlled, a main and a standby. The standby pump motor is considerably smaller than the main pump motor. The following controls are supplied for the two motors: One magnetic controller, one manual controller, and a four-position rotary selector switch. This last is for the purpose of manually selecting the motor to be used and the type of control, either automatic (magnetic) or manual. In addition, the selector switch is provided with a mechanically operated interlock switch which prevents the use of the selector switch while the circuit is energized. | ||
| In addition to its normal function, the magnetic controller is provided with a shaft extension and handwheel which permits use as a manual controller when the mechanically operated interlock switch is placed on "off" so that the control circuit is not energized. | ||
| When the plant is in use with either the manual or the emergency controller, the length of time the plant is in operation and hence the pressure in the system is governed by the operator. | ||
| The circuit fuses provide the only overload protection for the system. The magnetic controller is provided with a low voltage release relay and the manual controller is provided with a low voltage protective relay. In addition, the manual controller is provided with a holding magnet which also serves as a blowout coil. | ||
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| The magnetic controller is provided with two main contactor relays which function as follows: the coils of both relays are energized simultaneously upon the closure of the low voltage relay which in turn is energized or deenergized by the action of the contact makers associated with the accumulator. One of these relays is provided with a time delay device which operates on the oil dashpot principle and is adjustable between 4 and 10 seconds, remaining fixed at the desired setting. Thus, one contactor puts the motor across the line through the series connected starting field winding in the case of the main motor or the starting resistance in the case of the standby motor. When the time delay device allows the other contactor to close the motor is then connected across the line in its normal operating connection as a compound motor. A long wipe auxiliary contact on the second contactor deenergizes the first contactor and removes the starting component from the circuit. The long wipe contact prevents the circuit from being interrupted when transferring from the starting to the running position. | ||
| (b) Description | ||
| II. Motors | ||
| German motors are of the usual D.C. types, that is, constant speed shunt, adjustable speed shunt, constant speed compound and adjustable speed compound manufactured to operate over a voltage range of 110 to 170 volts. The design of a motor for a given load is less conservative than present U.S.N. practice. Full advantage is taken of the following factors which contribute materially to conserve space and weight required for his motors and controllers. | ||
| (1) He has designed his intermittent motor load requirements with considerably less factor of safety than present U.S.N. practice. | ||
| (2) He has taken full advantage of higher inrush currents, acceptable due to the use of a battery as a power supply (U.S.N. submarine auxiliary motor and controller specifications appear to be based on surface vessel practice in which the power supply of obtained from rotating equipments and it is desirable to limit the instantaneous loads to minimize the possibility of the control circuits opening.) | ||
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| A comparison of several German motors with the U.S.N. motors used on the corresponding systems is presented to bring out the differences in intermittent load practices as well as weight and space requirements of both equipments. | ||||||||||||||||||||||||||||||||||||||
Hydraulic Pump Motors |
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| Mote: German accumulator capacity 14,300 cubic inches, for use at variable pressures, U.S.N. accumulator capacity 2500 cubic inches, for use at constant pressure. | ||||||||||||||||||||||||||||||||||||||
Main Pump Motor |
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Standby Hydraulic Pump Motors |
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High Pressure Air Compressor Motor |
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| In the foregoing comparisons it is to be remembered that low voltage motors are ordinarily expected to be heavier than higher voltage motors due to the necessary increase in length of the commutator and increased size of armature copper. | ||||||||||||||||||||||||||||||||||||||
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| Contributing to the favorable balance of unit weights of the German motors are the following factors. | ||
| (1) Use of aluminum (or other light weight metals) for motor ventilation blowers, terminal boxes, and bells, etc. | ||
| (2) Working coppers and magnetic iron at higher densities. | ||
| (3) Paying detailed attention to the ventilation of all parts of the motor. Practically all motors are provided with blowers, and various methods including built-in ducting, directing vanes, etc. are used to insure air flow to all parts of the motor. | ||
| (4) Using smaller electrical clearances between polarities, polarities and ground, as well as apparently decreased factors of safety with regard to dielectric strengths of insulating materials by reducing thickness applied. | ||
| Counterbalancing some of the above items which should tend to make German motors heavier per unit weight are: | ||
| (1) Operating at voltages of approximately one-half those of U.S.N. motors. | ||
| (2) The use of built-in series starting windings which serve no useful purpose after the motor has accelerated, being cut out of the circuit. | ||
| Inspection of German motors reveals the following physical characteristics: | ||
| (1) The motors were of compact design, being either drip-proof or watertight as the installation required. | ||
| (2) Brush rigging is considered poor in that brush holders were usually mounted as a cantilever. The brushes are mounted radially, tension being obtained by use of flat spiral springs. Brush tension is adjustable by means of a keyed washer, the effect being much the same as in U.S.N. practice. Brushes are of the short "life" type, being less in length than U.S.N. brushes. This "shortness" minimizes the effect of rocking (hence, arcing) due to external vibrational disturbances. Brush stops to prevent loss of contact with the commutator under shock conditions are not used. | ||
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| (3) All motors are provided with capacitors connected across the brushes, two being connected in series across the brushes. The midtap between the capacitors is connected to the motor frame, which was grounded. These serve the purpose of arc suppressors at the brushes to minimize the wear on the commutator and to minimize the interference effect in electronic circuits. | ||
| (4) All motors are provided with terminal boxes installed at the point of manufacture. These boxes provide easy access for installation and maintenance. As nearly as can be determined, present U.S.N. submarine motors are delivered for installation requiring external connections. However, the installing yards usually add terminal boxes that correspond to the German application. In addition, the German terminal boxes are provided with patch plates on which the tube terminals are attached. The advantages of this feature are the same as for controllers. | ||
| (5) The German method of taking the leads from the terminal box within the motor frame is poor in that the phenolic bushing intended to protect the leads from the sharp edges of hole in the frame has frequently been found to have vibrated free, thus exposing the insulation of the leads to abrasive action. | ||
| (6) For quick stopping of a motor the dynamic braking principle is employed. | ||
| (7) Molded commutators are used more extensively than in U.S.N. practice and on motors up to 10 H.P. capacity. U.S.N. practice seems to limit this application to fractional H.P. motors. | ||
| (8) The physical spacing of the main poles and interpoles is such that only mechanical clearance is provided. In addition, there appears to be less iron in the core bodies for comparable motors. The physical spacing of the main poles and interpoles in close proximity to each other effectively increases the mass effect of motor frame with regard to the vibratory forces acting upon it due to the rotation of the armature and magnetic forces. This would tend to make the German motors operate more quietly with regard to the level of the sound energy transmitted to the hull and hence to the water. | ||
| (9) The thickness of the magnet frame is much less than on most U.S.N. motors of comparable size. | ||
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| (10) In many cases, the insulation used on armature windings is asbestos based (similar to our Delta Beston) relatively high operating temperature type. | ||
| (11) In general, ball bearings have been used throughout; however, a trend toward sleeve bearings is observed, this being desirable with regard to reducing the vibration sound transmitted to the water. Report 2G-9C-S40 points out that the German was familiar with this fact from a silencing viewpoint; in addition, he was aware that ball bearings become increasingly noisier with wear. | ||
| (12) There were no motors observed with herringboned armatures or pole pieces to minimize the possibility of the rapidly varying magnetic forces existing between the armature and pole pieces coming into resonance with one of natural frequencies of the motor frame. This feature was incorporated in individual cases on later type vessels, as described in the appropriate section for such vessels, and is used in U.S.N. submarine main motors. | ||
| (13) Practically all motors are mounted on bonded rubber mounts for sound isolation purposes. These mounts are generally used in compression; however, some are used in sheer, surprisingly, from the overhead. Snubbers or locking devices are not employed. Under shock conditions the load is borne by the bond of the rubber in one or more directions. | ||
| (14) Aluminum alloys were used extensively for end bells, blower fans, terminal boxes, covers, etc. where possible. These parts were either sand cast, fabricated or die cast. However, as late as 1940 the German plans and specifications indicate these parts were to be composed of black or grey cast iron, indicating that shock conditions had not been studied too seriously. Later specifications require the use of light-weight aluminum alloys for these parts. The alloys specified are German Navy specification numbers KM9302 to 9306 inclusive. | ||
| (15) The blower fans are usually mounted on the back of the motor (End opposite commutator). | ||
| (16) Grease cups and various types of rubber, or in some cases felt, retainer assemblies provide for the lubrication of the various bearings used in motors. | ||
| With regard to the German use of the series connected starting winding, the following is quoted from page 185 of "Control of Electric Motors" by P.B. Harwood (2nd Edition). | ||
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| "If rapid acceleration is desired, and relatively constant running speed, a compound motor should be used, and the series field might be cut out of the circuit after the motor has accelerated. This is the usual practice for elevator installations". | ||
| The German has incorporated the above described feature in many of his motors with the following exception; he does not limit himself to ending up with a shunt motor. In most cases, in fact, his motors operate as compound motors. In these motors a suitable starting winding is built in the motor which after the motor has accelerated sufficiently, is cut out of the circuit by means of the associated controller either manually or automatically while, at the same time the series winding for giving the desired compounding under the operating conditions is cut in. The starting winding serves no useful purpose during the operating period. | ||
| Shop tests were run on several German motors and controllers to determine the effectiveness of the series starting winding. These tests indicate that the starting winding performs satisfactorily, the motor accelerating smoothly without excessive arching between the commutator and brushes. | ||
| A starting test on a German hull ventilation blower motor and controller rated at 10.2/16.7 H.P.; 110/170 V; 89/90 Amps; 2400/3400 R.P.M. was made using 116 V DC power supply. (The blower housing was not in place, thus causing the motor to start under approximately 25% overload). | ||
| Starting with a maximum shunt field the motor accelerated to a final running speed of 1992 R.P.M. in 2.5 seconds. The flush current cycle was 150 to 45 amperes on the starting winding then 150 to 110 amperes on the running winding after the starting winding was cut out. The flush currents decayed in less than .25 of a second. | ||
| A shunt field rheostat was added to get an indication of the starting condition with less than full field. The rheostat was set to start the motor so as to attain a final speed of 2500 R.P.M. | ||
| The motor accelerated smoothly to this speed in 5 seconds. The flush current cycle was 150 to 35 amperes on the starting winding then 150 to 110 amperes on the running winding after the starting winding was cut out. The flush currents delayed in less than .25 of a second. | ||
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| The ohmic resistance of the starting winding in the motor is on the order of one quarter of an ohm. | ||
| Observation of motors removed for cleaning and general overhaul in the yard indicated that the motors are in no worse condition than comparable U.S.N. auxiliary motors removed for cleaning and overhaul; nor are they any more difficult to work on. | ||
| Interrogation of U.S.N. personnel who operated the German vessels indicated that electrical maintenance with regard to motors and controllers has been negligible and that the equipments operated satisfactorily. | ||
| (c) Recommendations | ||
| It is recommended that several German motors and controllers be given laboratory tests to more fully determine the causes for the light unit weights and compactness, as well as their limitations. In such tests it would be desirable to determine the actual flux densities used in their magnetic circuits and if these findings are favorable, to analyze the steels used. | ||
| In addition, it is believed that the series starting winding for rapid acceleration could be considered to advantage in connection with future designs using a battery for a power supply, since the relatively small instantaneous added load on the batter should not be objectionable. | ||
| (d) Conclusions | ||
| Basically, the German application of auxiliary motors and their associated control differ from present U.S.N. practice in that he depends to a much larger extent upon ship's personnel for satisfactory starting and operating his equipments. This basic difference has led to greater simplicity in circuit components with attendant decreases in maintenance, probabilities of failures, and - additionally - , by paying strict attention to small details - space and weight savings which when integrated over the entire auxiliary system are of considerable magnitude. | ||
| The ideas employed are not necessarily new - however, he has grouped them successfully to his advantage. | ||
| If one were to accept his concept of controller and motor application as being desirable, the German had advanced to a degree worthy of detail study as a guide from | ||
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| which equipments could be built to U.S.N. specifications. Particularly noteworthy is his willingness to accept high inrush currents (flush) during the starting cycle. This contributes heavily to the smallness of his controllers both manual and magnetic. | ||
| (e) Main Motors | ||
| The propulsion plant built in these vessels is a direct drive arrangement as opposed to electric drive. The Diesel engines and motors are clutched directly to the line shaft. Several design and construction details, both as to general arrangement and as to manufacture of the individual motors offer interesting points for study. These features are discussed in detail in Nav Tech Report 303-45 and in the German instruction book "Beschreibung und Betriebvorschrift der E Antriebanlage U Boote Typ IXC/40" (Descriptive and Operational Data of the Electrical Machinery, U Boats Type IXC/40) THe above information when correlated with the reports to be written by the USN operating personnel of the U-858 and the Board of Inspection and Survey should enable one to completely evaluate the electrical portion of this propulsion plant. | ||
May, 1946 |
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PORTSMOUTH NAVAL SHIPYARD, PORTSMOUTH, N. H. |
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