3 Phase Main Power Distribution

 

This document shows a suggested 3 phase main power distribution arrangement that has been operating in at least one car for many years. It is fairly simple and trouble free. Power selection can be manual or automatic. Three sources of power (480V trainline, 240V standby and 240V diesel generator) are used, with the cheapest source of power being automatically selected in that mode. Provision is also made to trainline the diesel generator, in cases where it is desirable to supply a neighbouring car with power (this feature is controlled by a keylock switch).

Two common voltages were picked for the car's wiring: 240V 3 phase for the heavier loads (e.g. motors, heating, airconditioning); 120/208V for the lighter loads (e.g. lighting, outlets, most appliances). Two sets of transformers convert the power from 480V to 240V and from 240V Delta to 120/208V Wye. Should you wish to eliminate the requirement for 240V standby power (it is increasingly rare to find this power provided), you could wire all of the heavy loads at 480V, thereby eliminating the larger set of transformers. The main drawing provided is color coded so that elimination of one particular feature is fairly straightforward.

The drawing Electric_3PhPower can be downloaded as a PDF. This drawing shows a schematic of the entire 3 phase power distribution circuit plus much of the control circuitry.

The wiring for the system power monitoring instrumentation (ammeter, voltmeter and frequency meter) can be found in the drawing Electric_PwrMon. You may or may not wish to include this portion of the system in your car but I'd advise that you do because it is very useful to help you understand what is going on and where the power is going, especially if problems arise.

Sources of Supply

Here are some useful links to the main components mentioned in the drawings. Naturally, substitutions are possible (just observe the correct voltages, current and other pertinent ratings) but you may wish to use the components specified, in which case, knowing where to look for them is half the battle.

A Square D I-Line Panel Board is used to distribute the 240V power. This panel uses FA Molded Case Circuit Breakers for loads up to 100 amperes.

A Square D NQOD Panel Board is used to distribute the 120/208V power. This panel uses QOB Bolt-on Circuit Breakers.

Three single phase, Square D Resin Filled Transformers were chosen to implement each of the 3 phase transformers, as they were easier to fit underneath the railway car. Incidentally, if you're looking to save money and are willing to work with used transformers (they seldom, if ever go bad), contact GN Trains and we may be able to help you save quite a bit of money.

The low voltage Control Power Transformers provide 24 volts for the control wiring. The Switches (no the link is not a mistake -- the selector switches are with the pushbuttons) and Pushbuttons chosen have large handles and buttons meant to be used by an operator wearing gloves (as is common in the railway profession).

Operation of Power Interlock

There are three sources of power available to the car (480V trainline, 240V diesel and 240V standby). At any one time, it is imperative that only one source be used to supply the power requirements of the car (if two sources were ever connected simultaneously, they would have to be properly phased to avoid causing an instantaneous overload at connection time). In normal use, it is not possible to prevent more than one source of power from being present at any one time (e.g. 480V trainline may be plugged in while the diesel is running) so the control circuits are designed to only select a single source of power, regardless of how many sources are available.

The 240/480V Power Interlock circuits attempt to make it impossible to connect more than one source of power to the car at any one time (Iím sure there is a fool out there whoíll figure out a way around the interlocks so I wonít go so far as to call them foolproof). There is also a provision made to trainline the diesel through the 480/240V transformers, should the need arise to supply another PV from the carís diesel through the trainline (this is a potentially dangerous procedure when personnel unfamiliar with the car are present, since they are apt to assume that a standing PV wonít have power on the trainline plugs unless they are connected to some external source. Also, the trainline complete circuit isnít utilized to monitor the trainline so it is possible to have live receptacles or plugs when they arenít expected. Consequently, this feature should be used only when absolutely necessary and then all receptacles and plugs should be tagged with a sign indicating the situation).

The following sections describe the operation of the interlock circuits and how they connect each power source to the car. First manual operation will be described, then automatic operation and finally the procedure for trainlining the diesel will be described.

240V Standby

When the 240V standby plug is inserted into either the left or right-hand receptacle, 240V power appears at CB1. Assuming that CB1 is closed, power passes through to CT1 and PH1. If the power is properly phased, PH1 closes. If not, the phase rotation may be reversed by throwing phase reversal switch SW4. At the same time, power is applied to the control pins of the two standby receptacles, the contacts of TD1 and one side of the coil of CT1. If the standby plug is properly inserted into the receptacle, the control contacts are jumped and power is applied to T1 which produces 24V. Pilot P1 lights indicating the presence of standby power, 24V is applied to the contacts of PH1 and pilot P8 lights, if phase relay PH1 is closed, indicating that the power is properly phased.

The 24V is fed from the contacts of PH1 to switch SW1. If SW1 is in the Standby position and assuming that SW6 is in the Manual (open) position, 24V is fed to RY9 which closes and thence through the contacts RY9A to TD1 and P4. Pilot P4 illuminates indicating that the standby power is selected and TD1 is energized. When the interval (approximately one second) selected by time delay relay TD1 expires, contacts TD1A close and main contactor CT1 is energized. Power flows through the contacts of CT1 to the main distribution panel.

The time delay for TD1 is set at approximately one second for two reasons. The first is to ensure that two sources of power can never be applied to the car at once, even when changing the power supply selection (this allows for contactor latency, etc.). The second is to avoid arcing and contactor bounce when the standby plug is inadvertently ripped from its socket (I leave it to your imagination as to how this could possibly happen) while the car is drawing power. The control pins of the standby socket are slightly shorter than the power pins and, when the plug is withdrawn, contact is broken on them before contact on the main power pins is broken. The contactor opens, removing the load from the standby power source and preventing arcing, if the plug is withdrawn completely. Meanwhile, TD1 will not close again for one second, thereby preventing contactor bounce as the plug is withdrawn (bounce could significantly reduce the life of the main contacts so avoiding it is desirable).

480V Trainline

When the 480V trainline connection is made, 480V power appears at CB2. Assuming that CB2 is closed, power passes through to PH2 and the contacts of RY1. If the power is properly phased (which it should always be because Amtrak never screws up), PH2 closes. At the same time, power is applied to T2 which produces 24V. Pilot P2 lights indicating the presence of trainline power, 24V is applied to TD4 (thereby preventing the diesel from being trainlined) and the contacts of PH2 and pilot P9 lights, if phase relay PH2 is closed, indicating that the power is properly phased.

The 24V is fed from the contacts of PH2 to switch SW1. If SW1 is in the Trainline position and assuming that SW6 is in the Manual (open) position, 24V is fed to RY8, TD2 and P5. Pilot P5 illuminates indicating that trainline power is selected and TD2 is energized (RY8 has no significant role in the operation of manual power selection). When the interval (determined as specified by Amtrak, see below) selected by time delay relay TD2 expires, contacts TD2A close and relay RY1 is energized (the role of RY1 is simply to repeat TD2 but at the higher voltage required by the coil of CT2). When the contacts of RY1 close, main contactor CT2 is energized and power flows through the contacts of CT2 to transformers T21, T22 and T23. These three transformers form a three phase delta transformer that steps down the 480V to 240V. From here the 240V is fed to the main distribution panel.

The time delay for TD2 is set at an interval prescribed by Amtrak, based on the carís number (it should be set to a minimum of one second, regardless of what Amtrak advises). The delay provided by TD2 is necessary for two reasons. The first is to ensure that two sources of power can never be applied to the car at once, even when changing the power supply selection (this allows for contactor latency, etc.), hence the minimum one second rule. The second is to prevent all of the car loads in an entire train from switching on immediately as soon as power appears on the trainline. The intervals for each carís delay are selected based on the car number. Since no two car numbers are identical and cars are assigned to a train at random, it is very improbable that an entire train will be made up of cars whose loads switch on all at once. Instead, when trainline power becomes available, car loads will sequence on gradually and provide a soft start for the HEP unit.

240V Diesel

When the diesel generator is running, 240V power is present at CB3. Assuming that CB3 is closed, power passes through to CT3 and PH3. If the power is properly phased (it is hard to imagine that it could be otherwise, but one never knows, do one), PH3 closes. At the same time, power is applied to the contacts of TD3, one side of the coil of CT3 and T3 which produces 24V. Pilot P3 lights indicating the presence of power from the diesel, 24V is applied to the contacts of PH3 and pilot P10 lights, if phase relay PH3 is closed, indicating that the power is properly phased.

The 24V is fed from the contacts of PH3 to switch SW1. If SW1 is in the Diesel position and assuming that SW6 is in the Manual (open) position, 24V is fed to TD3 and P6. Pilot P6 illuminates indicating that diesel power is selected and TD3 is energized. When the interval (approximately one second) selected by time delay relay TD3 expires, contacts TD3A close and main contactor CT3 is energized. Power flows through the contacts of CT3 to the main distribution panel.

The time delay for TD3 is set at approximately one second to ensure that two sources of power can never be applied to the car at once, even when changing the power supply selection (this allows for contactor latency, etc.).

Note that phase relay PH3 also detects under- and over-voltage conditions as well as phase rotation and phase loss errors. While the latter two are extremely unlikely, the former two could result from the generator exciter being adjusted improperly. If either of these two conditions occurs, see the exciter controllerís adjustment instructions provided by the manufacturer of the generator. Also note that under-voltage conditions could occur if loads that are too large are being applied instantaneously to the generator and that frequency problems (not detected automatically) could occur if the diesel engine governor is not set properly (see governor adjustment instructions provided by the manufacturer of the diesel engine).

Automatic Power Selection

Closing switch SW6 enables automatic power selection. In this mode the power interlock circuits disregard the setting of the Power Source selector switch SW1. Instead relays RY8 and RY9 monitor the available power and select the cheapest source (the cost of power is assumed to increase from cheapest to most expensive in the order of: trainline; standby; diesel) to be used by the car.

If the diesel is running but no other sources of power are available, relays RY8 and RY9 are not energized and the 24V control power passes through normally closed contacts RY8B and RY9B to operate time delay relay TD3. After its normal delay expires, TD3 closes and causes CT3 to close, thereby selecting the diesel as the power source for the car.

Regardless of whether the diesel is running, if standby power is available and 480V power is not available, relay RY9 is energized through RY8A and 24V control power is removed from TD3 because RY9B opens. Thus, the diesel is deselected by the application of standby power. Furthermore, 24V control power passes through RY9A and is applied to TD1. After TD1ís delay expires, TD1 closes and applies power to CT1 which also closes and selects standby power as the power source.

Once again, regardless of whether the diesel is running and also regardless of whether standby power is available, if 480V trainline power is available, relay RY8 is energized and 24V control power is removed from both TD1 and TD3 because RY8A and RY8B open. Thus, both the diesel and the standby power are deselected. In addition, 24V control power is applied to TD2. Once TD2ís interval expires, TD2 is energized closing contacts TD2A through which relay RY1 is energized (the role of RY1 is simply to repeat TD2 but at the higher voltage required by the coil of CT2). When the contacts of RY1 close, main contactor CT2 is energized and the 480V trainline power is selected.

As noted in the above sections about manual power selection, the time delay relays TD1, TD2 and TD3 are in the interlock circuit to prevent more one than one power source from being physically connected to the car at one time. In manual mode, these time delays allow for contact overlap (make before break) of the selector switch as well as main contactor latency. The time delays are just as important in automatic mode where they compensate for contact bounce in the control relays as well as contactor latency.

Trainlining the Diesel

Should an operational condition arise where it is necessary to trainline the diesel (e.g. to provide power to an adjacent, disabled PV), the power interlock circuits will allow this to be done. To begin this procedure, first ensure that only the car or cars to be supplied with power are plugged into the trainline receptacles. All other unused plugs and receptacles should be short-looped or bagged and then tagged to indicate that they are live (note that the trainline interlock circuits are not used so an unconnected connector or receptacle is not detected). Second, place the mode switch SW6 in Manual mode and the Power Source switch SW1 in the Diesel position. Start the diesel and move keyswitch SW2 to the Trainline position.

Trainlining of the diesel works in the following manner. When the diesel is running 240V power is present at CB3. Assuming CB3 is closed, 24V is generated by T3 and supplied to the interlock circuits. Placing SW1 in the Diesel position and SW6 in the Manual position routes the 24V to TD3 which closes in due course and operates CT3. CT3 closes and applies the diesel power to the car.

Applying power to the car causes 480V to appear at the back side of CT2 (a condition that one should be wary of when working on the carís electrical system) because transformers T21, T22 and T23 are permanently connected to the 240V buss. This 480V power is applied to contacts RY2A/B.

Closing switch SW2 with the key causes RY2 and RY3 to be energized through contacts TD4A. This causes RY3 to latch through holding contacts RY3A ensuring that the diesel remains trainlined until SW2 is opened or the diesel power is removed. Meanwhile, contacts RY2A/B close and apply 480V to CT2 which closes and passes power out through CB2 to the trainline. Note that, as above, RY2 is only necessary to handle the higher coil voltage used by CT2.

Since it is imperative that there be no power present on the trainline before the diesel is trainlined, detection of this situation is provided by TD4. If power is present before attempting to trainline the diesel, TD4 will be energized and contact TD4A will be open. This will prevent the closure of SW2 from applying control power to RY2 and RY3. Of course, TD4 will also be energized when the diesel is trainlined but its time delay, which should be set to a quarter second, will give RY3 enough time to close. The holding contact RY3A will then maintain closure of RY2/3 and keep the diesel trainlined.