Coeficiente parcial para las acciones permanentes Pe o propio del hormigón

The information that is presented in the checklists and information tables has been assembled from SAES-P-116, 16-SAMSS-510, ANSI C37, GI-2.710, and related industry standards.

Figure 10 shows a table of Saudi Aramco general requirements for manually operated, dead-front, pad-mounted switches that are equipped with either separable connectors or other terminating means for ac systems.

General Requirements

Either separable connectors or other buyer specified means may be used to terminate the cable at a load interrupting switch.

All energized parts of a dead-front pad-mounted switchgear (PMSG) must be insulated and completely enclosed within a grounded shielded system when separable connectors are in place.

The Vendor must provide equipment that is sufficiently derated to operate at nameplate rating under the following temperature conditions (in addition to the temperature rise that is caused by Vendor's supplied equipment when it is operating at the nameplate rating):

• Monthly Normal Maximum Ambient Temperature: 45 deg C

• Enclosure Internal Temperature Rise Due to:

(a) Solar Effects: 8 deg C

(b) Internal Heater (if applicable): 3 deg C

Total 56 deg C

Equipment that is supplied in accordance with 16-SAMSS-510 must be protected from corrosion and operational failure when operating under the following conditions:

• Normal air-borne dust concentration must be considered as 1 mg/m3 with 95% of all dust particles being less than 20 micrometer diameter.

• Compounds present in the dust include those of sodium, calcium, magnesium, silicon, and aluminum.

• Other pollutants present (worst case): H(2)S 20 ppm, SO(2) 10 ppm, CO 75 ppm, (NO(x) 5 ppm, and hydrocarbons 100 ppm.

Figure 10: Saudi Aramco Requirements forPad-Mounted Switchgear with Load-Interrupting Switches

Figure 11 shows Saudi Aramco load interrupting switch voltage ratings.

Rated Maximum Voltage (kV) Rated Withstand Impulse 3 ø Switches 1 ø Switches Voltage, kV

15.5 8.9 95

27 15.5 125

38 21.9 150

Figure 11: Voltages and Insulation Levels for Load Interrupting Switches (From ANSI C37.72 - 1987)

Figure 12 shows Saudi Aramco load interrupting switch load, cable charging, and magnetizing interrupting ratings. Figure 12: Load, Cable Charging, and Interrupting Current Ratings

(From ANSI C37.72 - 1987)

Figure 13 shows a table of Saudi Aramco guidelines for the application and the selection of load interrupting switches.

General Requirements

Load interrupting switches must not be used except with the prior written approval of the Manager, Saudi Aramco Power Distribution Department.

Pad-mounted switchgear (PMSG) with load interrupting switches must be designed, rated, manufactured, and tested in accordance with the latest issue or revision of ANSI/IEEE Standard C37.72 - 1987 or IEC 298.

Rated insulation levels and current ratings that are applicable to air switches must be in accordance with ANSI C37.32 or IEC 298.

All switches must be group-operated.

Switch operating mechanisms must be protected from damage due to weather, dust, and corrosion. For outdoor units, the switch mechanisms, linkages, and springs should be located inside tanks or enclosures.

Synchronism check devices must be provided in situations where it is possible to interconnect two systems out of synchronism.

For industrial applications, a blown fuse should initiate the opening of an associated switch.

Switches must be of dead-front construction.

Operational Requirements

Load interrupting switches must be capable of breaking currents that are equal to the continuous current rating of the switch at the rated system voltage and load.

Load interrupting switches must be capable of interrupting small inductive or capacitive currents for applications in which the switch is used to disconnect unloaded transformers, cables, or overhead lines.

Load interrupting switches must be capable of performing a closing operation onto a terminal short circuit.

Load interrupting switches must have independent operators.

Figure 13: Guidelines for the Application and Selection of Load Interrupting Switches

Figure 14 shows the construction requirements for medium and high voltage switch types from 16-SAMSS-510, ANSI C37.72 - 1987, and ANSI C37.32.

Frame-Mounted Load

The frame-mounted load interrupting switch (oil-filled) is only suitable for outdoor use.

Interrupting Cable terminations must be of dry-type, dead-front construction.

Switch Potheads must not be used.

(Oil-Filled) The cable type must be specified by the purchaser so the switch manufacturer can furnish the correct terminal parts.

For high making and breaking capacity, the switch must incorporate either a spring toggle mechanism or some form of arc control.

Regular maintenance of this type of switch is necessary to remove accumulated sludge and to test the quality of the oil.

Askarel or any polychlorinated biphenyl (PCB) dielectric (insulating fluid) must not be used.

Pad-Mounted Switches

Refer to 16-SAMSS-510 for pad-mounted load interrupting switch specification requirements.

Pad-mounted switchgear that uses switches in gas-filled sealed tanks is preferred over air-insulated switchgear.

Vacuum switches are the preferred type of switching device in pad-mounted switchgear.

Cable terminations must be dead-front, 600 A, separable, insulated connectors (elbows).

Two threaded 1/2 in., #13 National Course (NC) bosses must be provided at opposite sides of the enclosure.

Switch operating handles must be able to be padlocked in any position.

Switchways must be provided with three positions.

For switches that have on, off, and ground positions, the ground position must have the same withstand rating as the main switch.

The switch mechanism must be such that switching from on directly to ground is not possible. Switching must be from on to off and then from off to ground. A separate interlocked ground switch may be provided to meet this switch mechanism requirement.

The moving parts of switch operating mechanisms (e.g., springs) must be located inside the switch enclosure and protected from exterior

environmental conditions.

Pad-Mounted Switches

Bolts, hinges, and associated hardware must be of Type 300 Series stainless steel.

(Continued) Mounting frames and enclosing panels must be constructed of bolted galvanized steel.

Gasketing materials and adhesive must be suitable for the environmental conditions specified in 3.2.1.

All exterior surfaces must be painted and must meet the requirements of ANSI C57.12.28 - 1988, Pad-Mounted Equipment - Enclosure Integrity, Section 5 - Enclosure Coating System, except the paint color must preferably be white with light grey an acceptable alternative.

Nameplate(s) must be on the side of the enclosure.

The following information must be included and may be on a separate nameplate:

1) Buyer's purchase order number 2) Manufacturer's location

3) Manufacturer's order reference number

Nameplates must be in the English language according to American usage.

Danger and warning indicators must be written in both Arabic (Naskh script) and English, utilizing white characters on a red background.

Metal-Enclosed Interrupter Switchgear

Outdoor use of air-insulated interrupter switchgear is not allowed in new Saudi Aramco installations.

Figure 14: Construction Requirements for Medium and High Voltage Switch Types (Cont’d)

For consistency, rated insulation levels and fault-make ratings that are applicable to air switches (as defined in ANSI C37.32) must be used for loadbreak switches. Figure 15 shows the preferred ratings for medium- and high-voltage loadbreak switches that are used by Saudi Aramco.

Rated Withstand Voltage Current Rating (amperes, rms) Interrupting and Continuous

1 Short-time current ratings include a momentary and a three-second current rating that is based on test conditions that are described in section 5 of ANSI/IEEE C37.34. Divide the momentary rating by 1.6 to obtain the three-second current rating. When a higher momentary current rating than is shown is required, use a switch that has the next higher continuous current rating.

Figure 15: Load Interrupting Switch Preferred Ratings (From C37.32-1990)

Medium and High Voltage Load Interrupting Switch applications Checklist

Medium and high voltage switch rating information can be found on the equipment nameplate or in the switch manufacturer's technical manual. The following is a checklist that is used to verify that the type, the rating, and the operational characteristics of a switch are correct for the application based on Saudi Aramco and industry standards:

• Verify that the switch meets the Saudi Aramco requirements that are shown in Figures 13 and 14.

• Verify that the switch frequency rating is correct for the application.

• Verify that the switch rated maximum voltage is correct for the application:

- Rated continuous current at 60 Hz - Rated load interrupting current

- Rated momentary, making, and one-second current - Rated cable charging interrupting current

- Rated magnetizing interrupting current

• Verify that the switch impulse withstand voltage (BIL) is correct for the application.

• Verify that the switch operational characteristics will provide adequate protection for the electrical equipment that is in the circuit with the switch (e.g., fuse rating). Switch rating information can be found on the switch nameplate or in the manufacturer's technical manual.

WORK AID 2: REFERENCES FOR EVALUATING MOTOR VARIABLE SPEED