STAMFORD S7K Low Voltage Alternator 2700-3000 kVA

The S7K core: 3 MVA of alternator power in one frame

The STAMFORD S7K is the largest air-cooled low-voltage core in the S7 range, rated 2700 to 3000 kVA at 50 Hz (2160 to 2400 kW) and 2900 to 3600 kVA at 60 Hz (2330 to 2880 kW). STAMFORD introduces it as the latest addition to the S7 range, taking the S7 design to higher power density and performance and adding 300 kVA to the S7 line. It is aimed at prime power, standby, combined heat and power, grid and island-mode operation.

The brochure lists a 15 percent increase in power density and a 13 percent reduction in weight, describing the S7K as the lightest alternator currently available at this rating. The electromagnetic design works together with the patented CoreCooling system, which STAMFORD says delivers year-on-year fuel savings through higher efficiency, alongside industry-leading motor-starting capability.

Technical specifications

Factory options and accessories listed

Anti-condensation heater, quadrature droop kit, bearing RTD on each bearing, remote voltage trimmer, radio-frequency interference suppressor kit, excitation loss module, diode failure detector, winding RTDs and thermistors, and protection CTs. Also listed: current sensing kit, controlled short circuit, manual voltage regulator, frequency detection module, PFC3 power factor controller, remote control interface and an excitation circuit breaker.

Where the S7K fits in the S-Range

The S7K sits above the S6 for sets of roughly 2.5 to 3 MVA. The two figures printed in the brochure (2700 to 3000 kVA on the cover, up to 2800 kVA in the specification table) differ, so ask for the winding-specific rating sheet when sizing against an engine.

Large-alternator checklist

For machines of this size the main checks are engine torsional compatibility, bearing arrangement, terminal box position, cooling air path and protection scheme. The marine classification statement in the brochure says STAMFORD alternators meet the classification requirements of all major marine societies, and other certifications can be considered on request. A sleeve-bearing, two-bearing option is mentioned for the standard S7 marine machine. The brochure also prints support claims: a service network in over 120 countries, 24-hour dedicated service support, a 3-year warranty described as class-leading, and an authenticity guarantee through hologram verification.

How the STAMFORD S7K works

The engine turns the rotor of the alternator. A permanent magnet generator feeds the AVR, which controls the exciter field. The exciter output goes to the main rotor through rotating diodes. The AVR holds the output voltage as the load changes. Air is drawn through the machine to remove the heat.

Where the S7K is used

• Prime power plants
• Standby power plants
• Combined heat and power
• Grid-connected sets
• Island-mode operation

Selection checklist for the S7K

• Rating of 2700 to 3000 kVA at 50 Hz
• Rating at 60 Hz
• Voltage of 380 to 480 V
• AVR type
• Single or double bearing
• SAE adaptor
• Winding RTDs and heaters
• Engine type, diesel or gas

Installation, commissioning and maintenance notes for the S7K

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 winding and bearing sensors. Read the bearing temperatures during the first runs.

Requesting a quotation for the STAMFORD S7K

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.

S7K power at 50 Hz

The power at 50 Hz is 2160 to 2400 kW.

S7K power at 60 Hz

The power at 60 Hz is 2330 to 2880 kW.

S7K voltage range

The voltage range is 380 to 480 V.

S7K poles

It is a four-pole, wire wound machine.

S7K AVR

The AVR is the MX322 as standard, with the DM110, DECS100 and DECS150 as options.

S7K excitation

The excitation system is PMG.

S7K enclosure and cooling

The machine is rated IP23 and is air cooled to IC01.

S7K insulation

The insulation is class H.

Alternator records for the S7K

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

Choosing the right S7K options

Choose the heaters, the RTDs and the protection options that the site and the engine builder ask for.

S7K power density

The brochure lists a 15 percent rise in power density for the S7K.

S7K weight

The brochure lists a 13 percent cut in weight.

S7K prime movers

The alternator is made for diesel and gas engines.

S7K paralleling

The machine has paralleling capability.

Documents and quotation

Seven Star LLC supplies STAMFORD alternators, including S7K requests, against a full specification. Send kVA, voltage, frequency, engine make and model, duty and any grid-code or marine requirement. The brochure is linked here. See Diesel Generator Spare Parts for related generator components and the Cummins C1000D5B 1000 kVA diesel generator set for a smaller reference set. Confirm all ratings and drawings against the final data supplied with the quotation.

The brochure adds that the S7K is available with all the options and features of the S7 range, that it suits prime power, standby, combined heat and power, grid and island mode, and that full general-arrangement drawings can be downloaded from the maker website. Ask for the drawing that matches the final winding and bearing arrangement.