STAMFORD S6 Low Voltage Alternator 800-1400 kVA

Large-frame power for 1 MVA class generator sets

The STAMFORD S6 is the S-Range frame for 800 to 1400 kVA sets at 50 Hz (875 to 1694 kVA at 60 Hz), the size used in 1 MW containerised power plants, data-centre standby halls and oil and gas camp power stations. It is a four-pole wire-wound alternator with PMG excitation through the MX321 AVR, single-bearing construction as standard, and an output range of 380 to 690 V.

STAMFORD gives it enhanced thermal management, an optimised power-density core, a high-efficiency airflow path and two new core lengths at 1260 and 1400 kVA. An adaptor foot enables a switch between S5 and S6 frames, and a flexible foot lets the set base accept alternators from other makers.

Technical specifications

S6 Dedicated ratings, 400 V, 50 Hz, class H 125/40 (winding 311/312)

The G and H cores are not reconnectable. Marine ratings (class B, 50 degrees C ambient) are given separately in the brochure.

Choosing the voltage regulator and accessories

The brochure shows the MX321 supporting current sensing, controlled short circuit, manual voltage regulation, frequency detection, the PFC3 power factor controller, a remote control interface and an excitation circuit breaker. The MX341 offers the same list except controlled short circuit. DECS100 and DM110 digital regulators are shown as alternatives. Choose digital regulation where the set will be paralleled or must support grid-code functions.

Planning for a 1 MVA set

At this size the alternator frame, the engine adaptor and the terminal box position all need to be settled during set design. The brochure gives IP44 terminal box, bearing RTDs on each bearing, anti-condensation heater with terminal box, quadrature droop kit, RFI suppression and diode failure detection as factory options. The document is marked preliminary, so use confirmed GA drawings for baseplate design.

How the STAMFORD S6 works

The engine turns the rotor. The PMG gives power to the AVR, which feeds the exciter field. The exciter output goes to the main rotor through rotating diodes. The AVR holds the output voltage as the load changes. A fan draws air through the machine to remove the heat.

Where the S6 is used

• Containerised power plants of 1 MW
• Data-centre standby halls
• Oil and gas camp power stations
• Prime power plants
• Sets paralleled with others

Selection checklist for the S6

• Rating of 800 to 1400 kVA at 50 Hz
• Rating at 60 Hz
• Voltage of 380 to 690 V
• AVR: MX321, MX341, DECS100 or DM110
• Single or double bearing
• SAE adaptor
• Winding RTDs and thermistors
• Terminal box protection

Installation, commissioning and maintenance notes for the S6

Align the alternator with the engine and fix it on a rigid base. Keep the air inlet and outlet clear. Check the insulation resistance before the first start. Test the sensors and the AVR settings. Watch the bearing temperatures in the first runs.

Requesting a quotation for the STAMFORD S6

Please send the kVA, the frequency, the voltage and the options. Seven Star LLC serves industrial customers in Oman and the GCC and replies with a quotation based on the information provided.

S6 rating at 50 Hz

The rating at 50 Hz is 800 to 1400 kVA.

S6 rating at 60 Hz

The rating at 60 Hz is 875 to 1694 kVA.

S6 voltage range

The voltage range is 380 to 690 V.

S6 construction

It is a four-pole, wire wound machine with class H insulation.

S6 excitation

The excitation is the MX321 AVR with PMG.

S6 enclosure

The machine is rated IP23, with an IP44 terminal box as an option.

S6 cores

The dedicated cores run from C to H, with ratings from 810 to 1400 kVA at 400 V.

S6 feet

An adaptor foot allows a switch between S5 and S6 frames, and a flexible foot suits other makers.

Alternator records for the S6

Record the insulation resistance, the bearing temperatures and the date of each service.

Choosing the right S6 regulator

Choose a digital regulator where the set will be paralleled or must support grid-code functions.

S6 prime movers

The S6 is made for diesel and gas engines.

S6 terminals

The machine has 6 terminals and can be reconnected for three phase on most cores.

S6 voltage sensing

The sensing is three phase, with two phase as an option.

S6 thermal design

It has enhanced thermal management and a high-efficiency airflow path.

Documents and quotation

Seven Star LLC supplies STAMFORD S6 alternators on request from Muscat. Please send kVA, voltage, frequency, engine model and flywheel housing, AVR and options required, and whether the set is for standby or prime. Browse Diesel Generator Spare Parts for related generator parts, or see a 1 MVA reference such as the Cummins C1000D5B 1000 kVA diesel generator set. Verify winding and dimensions against final data before ordering.

The brochure also carries a separate S6 marine ratings section, states that all ratings and drawings are preliminary and subject to change, and notes that its general-arrangement drawing is indicative of the S6D-H core. Additional voltages can be requested from the maker applications department, so quote the exact voltage needed.