How to operate equipment requiring 2 single phase 120 volt lines in a warehouse.

[makiao1813]

Background info-I am trying to figure out how to operate a satellite terminal off of commercial shore power in a warehouse. The terminal typically uses a 7.5K or 10K generator, but the customer wants to make life easier. The terminal has 2, 120 volt lines, a neutral, and a ground. The warehouse has 120/208 line coming in. I am going to refer them to an electrician, but I would like to explain what is needed to make this happen. Take it easy on me, I have only taken basic electronics and deal with mostly RF theory and equipment operation.

 

[Smart $]

Without more info, all I can tell you that is needed is a transfer switch (automatic or manual?). Is the gennie 120/240 1? 3-wire or 208/120 3? 4-wire?

 

[suemarkp]

A lot of computers and network equipment have redundant power supplies. Not sure if this is the same, but if so you basically feed it with two circuits. If one dies, the other will power it. If both are live, generally both circuits draw half power. The intent is that one of the two circuits be generator, UPS, Emergency, or other power (at least from a different panel in case on has to be shut down). However, when I don't care about any of the redundancy, it gets one or two circuits. You may be able to put both power cords into a duplex receptacle on the same circuit.

You'd need to study the manual to determine the power requirements to see if you can power it from one circuit or two. And think about the availability of the sat receiver -- is it important that it be "up" as much as possible?

 

[hurk27]

It sound's like your saying normally this satellite transceiver station ( assuming because of power requirement) is run from a generator, and the customer wants to now run it from a utility source, if the generator is to be kept in line for back up when utility power is lost, then as was pointed out a transfer switch has to be used, sized for the loads it will be handling, to prevent the generator back feeding the utility (this is to prevent electrocuting line men thinking their lines are dead)

I think what we need to know is what is the required voltage, how much current is required, and it sounds like you saying that the equipment requires a 120/240 volt single phase supply (two hots and a neutral) if the equipment shares the neutral then there must be 240 volts between the two hot conductors (on opposite phases), but one thing you need to check! if the equipment requires 240 volts as well as 120 volts, you need to find out if it will operate at 208, if not you will need a 208 to 120/240 volt transformer sized for the load, or buck/boost transformers (which can cut cost).

 

[Electric-Light]

What are the specifications on the power supply?
Some server equipment with high power demand operate on 208v.
Normal stuff, including the average home computer are increasingly going to 96-264v switch-less power supply. In the past, power supplies often had 115/230.

You might as well just take two cords, then plug it into the same power strip unless you can provide each power supply reasonably independent source of power.

Even if you put them on different circuits, if you have a utility outage, you'll lose power to both circuits defeating the redundancy purpose.

You will need to use a UPS, probably a double conversion one, that can operate properly on generator power. Many UPS won't see generator power as clean enough and won't come out of battery power.

If you don't use a UPS, there is no way the computer can handle the transfer time.

 

[hurk27]

You will need to use a UPS, probably a double conversion one, that can operate properly on generator power. Many UPS won't see generator power as clean enough and won't come out of battery power. If you don't use a UPS, there is no way the computer can handle the transfer time.

Err a dual conversion UPS is always on battery power, utility just keeps the battery charged:roll:

 

[Electric-Light]

No, not really. The battery doesn't really do anything. Think of it like using an inverter in a car. Alternator provides the power and maintains battery voltage, but you're not putting power into battery, then drawing it back out of battery.

It converts the AC power to DC and inverter regenerates AC, so it will provide very high quality AC regardless of input power quality. When AC power is present, many do use the power line as timebase though, so devices that use AC line to keep time won't lose time. Though UPS itself have a crystal timebase, its not accurate enough for time keeping.

 

[makiao1813]

More info.....

More info.....

I guess I did not give all the required info. The satellite terminal is ruggized self sustainable mobile unit. It has 2 12v backup batteries in lieu of an UPS. It has two inverters for the AC to DC conversion in case of loss of AC to convert to the backup batteries. The back-up batteries are charged with an installed battery charger. All the equipment in the racks require 120v to operate. I believe it has two 120v lines as one is dedicated to the High Power Amplifier and the other line is for everything else, i.e. modem, router, media converter, laptop, etc. It has an on-board 7.5K generator that is supposed to be utilized as an Auxillary Power Unit and the systems is supposed to utilize a seperate 10K as it's main power supply. It is cabled into the generator with a pig-tail with the hot wires going to L1 and L3, and the neutral and ground connected to their respective positions. The warehouse has regular outlet connections of 120/208. The question is, what materials would be need to hook the pigtail up to the shore power of the warehouse. I think I better explained it this time. Let me know know if more info is needed!

 

[Smart $]

I guess I did not give all the required info. The satellite terminal is ruggized self sustainable mobile unit. It has 2 12v backup batteries in lieu of an UPS. It has two inverters for the AC to DC conversion in case of loss of AC to convert to the backup batteries. The back-up batteries are charged with an installed battery charger. All the equipment in the racks require 120v to operate. I believe it has two 120v lines as one is dedicated to the High Power Amplifier and the other line is for everything else, i.e. modem, router, media converter, laptop, etc. It has an on-board 7.5K generator that is supposed to be utilized as an Auxillary Power Unit and the systems is supposed to utilize a seperate 10K as it's main power supply. It is cabled into the generator with a pig-tail with the hot wires going to L1 and L3, and the neutral and ground connected to their respective positions. The warehouse has regular outlet connections of 120/208. The question is, what materials would be need to hook the pigtail up to the shore power of the warehouse. I think I better explained it this time. Let me know know if more info is needed!

Would need schematic or other documentation to confirm, but based on your posted info, the system may already contain the transfer switch and backup gennie controls (which you called the APU). Continuing on that assumption, it sounds as though all that needs provided is a "rated" 3-wire circuit from the 208/120 shore power system to a junction box, which the cable would then be hard-wired to the circuit conductors... or if the 208/120 panel is close enough, and the cable is of a type recognized by the NEC, the cable could be connected directly without having to run circuit conductors and installing the j-box.

Keep in mind the preceding is just an assumption. Need more info to make it any of it certain. Additionally, a load calculation would be required to determine if the shore power system has enough overhead to allow this tie-in.

 

[makiao1813]

Would need schematic or other documentation to confirm, but based on your posted info, the system may already contain the transfer switch and backup gennie controls (which you called the APU). Continuing on that assumption, it sounds as though all that needs provided is a "rated" 3-wire circuit from the 208/120 shore power system to a junction box, which the cable would then be hard-wired to the circuit conductors... or if the 208/120 panel is close enough, and the cable is of a type recognized by the NEC, the cable could be connected directly without having to run circuit conductors and installing the j-box.

Keep in mind the preceding is just an assumption. Need more info to make it any of it certain. Additionally, a load calculation would be required to determine if the shore power system has enough overhead to allow this tie-in.

Thank you, That is what is was thinking. A second opinion supporting my thoughts has me confident enough to brief the client. Of course, they will be using a real electrician to make this happen!

 

[gar]

110415-1243 EDT

Electric-Light:

Actually the floating battery between the AC to DC charging supply and the DC to AC inverter does actually perform a function and current flows in and out every 1/2 cycle. It looks like a big capacitor. Most likely there is not a very large series inductance in the AC to DC charging section and therefore current only flows on the peaks of the input AC voltage. While the DC to AC inverter will be drawing some current throughout the entire output 1/2 cycle.

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[Electric-Light]

110415-1243 EDT

Electric-Light:

Actually the floating battery between the AC to DC charging supply and the DC to AC inverter does actually perform a function and current flows in and out every 1/2 cycle. It looks like a big capacitor. Most likely there is not a very large series inductance in the AC to DC charging section and therefore current only flows on the peaks of the input AC voltage. While the DC to AC inverter will be drawing some current throughout the entire output 1/2 cycle.

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Only high-end UPSs are full-time(dual conversion) and they're used by customers who are billed power factor penalty, so most newer dual conversion UPS have active PFC on the front end.

The battery is not required when there is no outage and battery can be swapped hot at the risk that load will go down if a power failure coincides. Some UPS also have a bypass relay to tie the load directly to utility in case of inverter failure or surge load exceeding inverter capacity.

 

[Electric-Light]

The question is, what materials would be need to hook the pigtail up to the shore power of the warehouse.

Depending on distance and load characteristic of the power amplifier, it maybe best to use separate neutrals. If the satellite power amplifier is a pulsed load, every pulse load would cause the voltage to burp on the other side.

If you had instruments on one pole, power amplifier on the other pole in a shared neutral system, every bass boom would cause lights to brighten on instruments side. Dim on amplifier side feed. If you use separate neutrals, the disturbance would be mostly contained on amplifier side, so the lights and instruments can go on instruments side.

You described the power will be from 208Y/120 source which is on one common trip breaker. Since you're not making any use of 208v, you might not even need two circuits.

 

[gar]

110415-20326 EDT

Electric-Light:

Can you more completely describe the internal circuit in the dual conversion UPS to which you refer?

Are there two input converters? One to charge the battery and the other to directly supply the output converter? If that is the case, then what is used to isolate the battery from the output converter (inverter) until the parallel source loses power? Is it a simple diode or something else?

.

 

[Electric-Light]

110415-20326 EDT

Electric-Light:

Can you more completely describe the internal circuit in the dual conversion UPS to which you refer?

Are there two input converters? One to charge the battery and the other to directly supply the output converter? If that is the case, then what is used to isolate the battery from the output converter (inverter) until the parallel source loses power? Is it a simple diode or something else?

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It's a pretty intense reading:
http://www.apc.com/prod_docs/results.cfm?DocType=App Note&Query_Type=10

Read "understanding Delta conversion". The documents are scattered everywhere, but there are many parts to it.

Here's a quicker version:
http://www.apcmedia.com/salestools/SADE-5TNM3Y_R5_EN.pdf

Delta conversion is basically having power factor correction in front of the power supply feeding the inverter.

Anyways, its very much like the automotive electrical system. The alternator (which is three phase, so it doesn't really need "bulk storage capacitor" since the output never drops to zero) provides power for all the electrical loads + replenish the battery, but as you're driving, its not like the battery is getting charged and discharged. It simply provides a constant voltage source that is slightly higher than idle state of battery, thus providing charging to battery as well as electrical load.


American Power Conversion is quite protective of the exact schematic, so you're gonna have to find one to dissect if you want to figure out the specifics.

 

[gar]

110416-0820 EDT

Electric-Light:

In your discussion you switched from dual conversion to delta conversion.

Consider dual conversion and your analogy with an automotive system. If we had a DC generator, older automotive systems before about 1960, then:

If the system load is less the current limiting point of the voltage regulator package, which includes a current limiting relay, then current flows to the load and the battery with no current flow at all from the battery to the load.

If the generator goes into current limiting, and the voltage at the generator output is slightly less than the present battery voltage, then some of the load current flows from the battery.

Change to an alternator as the energy source. This is a three phase alternator with rectifiers to produce an average DC output. This does not provide the perfectly steady output of the DC generator. It has ripple. Depending upon the magnitude of the ripple, the load current, and the operation of the voltage regulator current limiter, in relation to the present battery voltage there are conditions where there will be a ripple current to and from the battery. If this were a single phase system the +/- ripple current would be greater.

In a dual conversion UPS system with input power present you could probably remove the battery and have it work especially if there is a moderate amount of capacitance in parallel with the battery.

In the delta system you referenced what happens with battery current under various input-output conditions is a very complex issue.

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[Electric-Light]

In the delta system you referenced what happens with battery current under various input-output conditions is a very complex issue.
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I don't know. Why don't you get one to autopsy? All I know is that battery can be switched while inverter is online with zero transfer time. How far the front-end converter will hold before losing regulation on DC bus to the point the rear-end can no longer sustain, I have no idea.