Forum Electric: Electrical forum, Electrical engineering, electrician, power plant, energetics,wires

JDLT · Joined: 20 Jun 2008 Posts: 1

Hi all

I am new to this forum.
I have a question that can seem easy to answer... let's see together

Let's imagine a diesel driving a generator.
Diesel rotation can change according to the order of sparking the pistons.

So, for a generator built according to IEC, the phase sequence will be
U -> V -> W when clockwise operation.

Code:

60034-8 (June 2007) Rotating Electrical Machines, Part 8: Terminal Marking and direction of rotation.
§ 5 states: "The direction of rotation shall be that of the shaft observed when facing the D-end."
§ 6.7.1 states: "The terminal marking shall be so arranged that clockwise rotation is obtained when the alphabetical sequence of the letters (for example, U1, V1, W1) corresponds to the time sequence of the system phase voltages. […]
For counter clockwise rotation, the time sequence of the system phase voltages shall be reversed by rearrangement of the supply cables (for example, L2 and L3 in the case of 3 phase).
The requirement in the clause applies to machines of any rated output and voltage even if clockwise rotation is impracticable."

IEC states it is mandatory to have a generator with U->V->W when clockwise. If you have a diesel turning clockwise (so generator counter-clockwise, the U->V->W phase sequence must obtained with cable cross connection.

But for a generator built according to IEEE, the phase sequence can be agreed between maker and customer, ie it can be U -> V -> W when counter-clockwise operation.

Code:

IEEE C50.13 (2005) Standard for Cylindrical-Rotor 50Hz and 60Hz Synchronous Generators Rated 10MVA and Above
§ 4.1.11 states: "Phase sequence defines the order in which the phase voltages reach their positive maximum at the terminals of a machine, and shall be agreed upon between the manufacturer and purchaser. Typically this is given as a three-letter sequence R, C, L (Right, Centre, Left) or L, C, R (Left, Centre, Right), as defined by an observer looking at the terminals from outside the machine. In the case of terminals on the top or bottom of the machine, the sequence is defined looking from the end of the machine nearest the terminals toward the centreline of the machine.
Care must be exercised to ensure that the defined phase sequence of the machine is consistent with that of the connected equipment, particularly in the situations where the plant layout requires otherwise identical machines to have different phase sequence."

I would like to know your experience.

What about : GE, Brush, Alstom, ABB, Siemens, etc. generators?
Are they all U->V->W when turning clockwise?
Do you specify them according to IEC or IEEE or NEMA...?

(I am talking about 10MVA generators, medium speed, not turbine-type generators in nuclear power plants)

Thank you