Overload Protection of Three-Phase Submersible Motors

The characteristics of submersible motors are different from standard, above ground motors. Submersible motors require special overload protection. In order to properly protect a three-phase submersible motor, ambient-compensated, quick-trip overload protection must be used. This can be either a fixed heater or adjustable overload relay, as long as it is ambient-compensated and quick-trip. Franklin Electric?s Subtrol-Plus system can also be used to protect Subtrol-equipped motors.

Ambient-Compensated: Ambient-compensated overload protection must be used to maintain protection in both high and low air temperature areas. Three-phase pump panels are typically suitable for indoor and outdoor applications within temperatures of +14°F (-10°C) to +122°F (50°C). Pump panels should never be mounted in direct sunlight or high temperature locations as this will cause unnecessary tripping of overload protectors. A ventilated enclosure, painted white to reflect heat, is recommended for outdoor high temperature locations.

Quick-Trip: If the motor is stalled or the shaft cannot turn, the overload protector must trip quickly to protect the motor?s windings. In some areas, it is customary to specify that the overload must trip within 10 seconds with 500% normal current (IN). Quick-trip heaters and overload relays shown here, will respond within 10 seconds. Franklin?s Subtrol-Plus responds within 3 seconds. Heaters marked ?Standard Trip? are typically Class 20 or 20 second response time. Standard Trip, Class 20 and some Class 10 overloads will allow submersible motor burn-out before tripping. Quick-trip overload protection must be used.

The time-current trip curve, as shown in Figure 1, shows the response time for different classes of overloads under different running scenarios. The bottom axis of the chart shows different multiples of normal currents. The side axis shows ?Time? in seconds. The first bold vertical line represents the amperage if the power source single-phases on the motor side of the transformer (secondary side). This can occur if a fuse blows or a contact fails. This condition causes the normal line amperage to increase to 173% of normal in two phases and drop to zero in the third phase. The second bold vertical line represents the amperage if the power source single-phases on the incoming side of the transformer (primary side). This can occur if a power line is broken in a storm or car accident. This condition causes the normal line amperage to increase to 230% of normal in one phase and 115% of normal in two phases. The third vertical line represents a locked rotor or bound shaft condition. As you can see from the motor burnout curve or shaded area, the motor must be disconnected with a quick-trip device or severe motor damage can occur. The best protection, as the bold horizontal line shows, is Franklin?s Subtrol-Plus which disconnects the power within 3 seconds.

Approved Overloads: A list of fixed heaters vs. motor size can be found on page 16 of Franklin?s 60 Hz Application Installation Maintenance (AIM) manual. The only fixed heaters currently approved for use with Franklin?s submersible motors are the Furnas ?K?, Allen-Bradley ?J?, and General Electric ?CR123-L? series. Fixed heaters not shown on page 16 are not approved to use with submersible motors because they are not ambient-compensated, quick-trip style.

In addition to fixed heaters, many acceptable adjustable overload relays are available. The types listed here and repeated on page 17 of the AIM manual will also protect a submersible motor. An installer should select the relay based on the set and maximum amperage ratings of the motor as shown in the heater tables and footnotes on pages 16 & 17. Optimum motor protection may be obtained by setting adjustable overload relays at 5% above actual motor amperage, especially when motors are lightly loaded.

Some approved overload relay types may only be available for part of the listed motor ratings. When relays are used with current transformers, relay setting is the specified amps divided by the transformer ratio. Most industrial control manufacturers take this into account when specifying heaters to be used in large starters which contain built-in current transformers or CT?s.

Approved Adjustable Overload Relays

ABB Type: RVH40, RVH65, RVP160, T25DU, T25CT

AEG Series: B17S, B27S, B27-2, B27T

AGUT: MT03, RIK1, RIL0, RIL3, TE set class 5

Allen Bradley: Bulletin 193 ?Bi-Metallic?

Automatic Switch Types: DQ, LR1-D, LR1-F, LR2-D13, LR2-D23, LR2-D33.

Bhartia C-H: MC 305 ANA 3

Clipsal: 6CTR, 6MTR

Cutler-Hammer: C316F, C316P, C316S, C310 time setting 6 sec. max.

Danfoss: T1-16, T1-25

Fanal Types: K7 or K7D through K400

Franklin Electric: Subtrol-Plus

Fuji Types: TR-0Q, TR-0QH, TR-2NQ, TR-3NQ, TR-4NQ, TR-6NQ,RCa3737-1CQ, RCa3737-1CQH

Furnas Types: US15 48AG, US15 48BG, ESP100 Class 10

General Electric: CR4G, CR7G, RT*1, RT*2, RT*4, RTF3, CR324X Class 10

Kasuga: RU Set Operating Time Code = 10 & time setting 6 sec. max.

Klockner-Moeller Types: Z00, Z1, Z4, PKZM1, PKZM3, PKZ2

Lovato: RC9, RC22, RC80, RF9, RF25, RF95

Matsushita: FKT-15N, 15GN, 15E, 15GE, FT-15N,FHT-15N

Mitsubishi: ET, TH-K12ABKP, TH-K20KF, TH-K20KP, TH-K20TAKF, TH-K60KF, TH-K60TAKF

Omron: K2CM Set Operating Time Code = 10 & time setting 6 sec. max., SE-KP24E time setting 6 sec. max.

Riken: PM1, PM3

Samwha: EOCRS Set for Class 5, EOCR-ST, EOCR-SE, EOCR-AT time setting 6 sec. max.

Siemens Types: 3UA50, 3UA52, 3UA54, 3UA55, 3UA58, 3UA59, 3UA60, 3UA61, 3UA62, 3UA66, 3UA68, 3UA70, 3VU13, 3VE, 3UB – Class 5

Sprecher & Schuh Types: CT, CT1, CTA1, CT3, CT6, KTA3, CEF1 time setting 6 sec. max., CET3 time setting 6 sec. max.

Square D: Class 9065 Types TD, TE, TF, TG, TJ, TK, TR, TJE, TJF Class 10, SS Class 10, SR Class 10. Integral 18, 32, 63

Telemecanique: Types LR1-D, LR1-F, LR2-D13, LR2-D23, LR2-D33, GV2-M, GV2-P, GV3-M (1.6 – 10 amp ranges only).

Toshiba Type: 2E RC820 time setting 8 sec. max.

Westinghouse Types: FT13, FT23, FT33, FT43, K7D, K27D, K67D, MOR, Advantage – Class 10, IQ500 – Class 5

Weg: RW2

Westmaster OLWR00, OLWT00 suffix D through P

Other relay types from these and other manufacturers may or may not provide acceptable protection. These should not be used without approval from Franklin Electric.

Franklin does not recommend selecting overloads larger than specified in Franklin?s Application Installation Maintenance manual.