Elevator electrical name plate 2

[james64]

Hello all,

I am currently designing an elevator and machine room for subway. Electrical specification say as below

MAXIMUM ALLOWABLE VOLTAGE VARIATION IS +/- 10% KONE CALC THE FOLLOWING FOR THIS ELEVATOR DUTY
NAME PLATE AMPS : 15
Max ACCEL AMPS : 26

PROTECTION DEVICE REQUIRED PRIOR TO INSTALLATION MAX MOTOR BRANCH SHORT-CIRCUIT PROTECTION IS

UL CLASS RK1 FUSE (AMP) : 20
SUPPLIED VOLTAGE : 600V, 3PH, 60HZ

I am confused as to the design for elevator load calculation to size generator. Because name plate, max accel ampere and fuse, all three number are different. Which ampere should I follow for load calculation?
Any knowledge on the subject will help or any reference as to where to learn more on this topic. Thank you!

 

[waross]

Fuse Amps: In North America i is common for air conditioning units to show on the nameplate the ampacity of the supply circuit as per he electrical codes.
When selecting a generator for a VFD driven motor, I would be guided by the acceleration Amps.
When selecting a generator for a DOL motor, I typically use three times the full load Amps.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[james64]

Thank Waross for your comment !!

 

[mc5w]

Part of what is confusing you is that time delay ( on overload ) fuses and circuit breakers were invented to allow motors to start without having to size the fuse of circuit breaker for say 1,400% of motor full load current.

The ability of a generator to start and run a motor depends on a few factors:

1. The ratio of saturation magnetism to magnetism at full load will limit how much peak current can be drawn from a generator. The really cheap kind of generators do not work so well for starting motors and in some cases locked rotor current or even the inrush current has to be below the full load rating of a CHEAP generator. Generally, the inrush current for a general purpose motor will be the greater of 1,400% of full load current or 200% of locked rotor current. Inrush current only lasts for about 1 cycle because the air gap and steel structure of the motor have almost zero energy stored in the magnetic field. The current then drops down to locked rotor and then the motor starts turning. As the motor accelerates the current goes down a little and then reaches a peak where the peak amount of torque that the motor can produce occurs. Caution: for a Design A low slip crusher duty motor the peak current at the torque peak is 1,400% of full load current because these motors have the ability to produce a LOT of peak torque.

2. The ability of the alternator to supply reactive a.k.a. magnetizing current varies from very little for a 100% power factor alternator to 60% of full load current for an 80% power factor rated alternator. When a motor draws reactive current from a generator the exciter has to inject MORE direct current into the rotor of the alternator.

Most single phase alternators are rated 100% power factor and how much reactive current it can supply can vary from a little to a modest amount IF the total current drawn is say 80% of the rating of the alternator.

If you are running a lot of single phase motors a possibility is to hook up an 80% 3-phase alternator to act as 3 single phase alternators what is known as 120/208/240 volts 7-wire 6-phase. Some electrical utilities support this as a service supplied system.

 

[waross]

2. The ability of the alternator to supply reactive a.k.a. magnetizing current varies from very little for a 100% power factor alternator to 60% of full load current for an 80% power factor rated alternator.

Not quite.
Alternators or generator ends are rated in KVA. That is an expression of the maximum allowable current times the working voltage.
The KiloWatt rating is a reflection of the power of the prime mover.
Typical industrial loads run at about 80% power factor.
It is common practice to undersize the prime mover.
The power factor of a load is the ratio of real power over apparent power.
The power factor rating of a set is a ratio of the mechanical kW of the prime mover over the KVA rating of the generator end.
It has nothing to do with an ability to produce reactive power.

A 100 KVA set is typically driven by a prime mover rated at 80 mechanical kW.
80 kW / 100 KVA = 0.8 PF.

By the way, I would like to see a vector sketch of the 7 wire 120/208/240 Volt supply.
Actually, I know a circuit to get those voltages from the same generator.
In fact, if a 10 lead generator is configured for true single phase with a Collin connection, you may pull off that combination of voltages with five wires.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[waross]

It is very rare to see a single phase alternator above about 20 KVA.
There are some specially built for military contracts but no one else uses them.
Almost all 1800 RPM sets above about 20 KVA are reconnected three phase sets.
When a set is reconnected from three phase to single phase, you lose 1/3 of the KVA rating.
The engine is not changed.
So a set rated at 75 KVA and 0.8 PF as a three phase set has a prime mover of 60 mechanical Kw.
If that set is reconnected for single phase, the KVA rating drops to 50 KVA.
50 KVA driven by a prime mover of 60 mechanical kW has a PF of 1.0 and is overpowered.


--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[james64]

Thank you all !!