Project record · Kazakhstan · River-port pump station · Submersible pump on a VFD

Medium-Voltage Submersible Pump Cable Replacement at a River Port in Kazakhstan: 180 m of 6/10 kV Cable in One Length

A river-port pump station in Pavlodar, Kazakhstan, needed a medium-voltage submersible pump cable replacement for a 6000 V submersible pump fed from a medium-voltage variable-frequency drive (VFD) through a du/dt filter. TEBAOFLEX supplied 180 m of (N)TSCGEWCUEUS 6/10 kV S3×50+2×25/2+S(4×0.5), ordered as one continuous length on one drum without joints. The cable has three 50 mm² power cores, two 12.5 mm² earth cores, two twisted control pairs under a common screen, an overall tinned copper braid and a red rubber sheath, with an agreed maximum outside diameter of 54 mm to fit the pump's cable entry. The factory acceptance test criteria agreed with the buyer include partial discharge of 10 pC or less at 1.73 U₀, and the drum has shipped.

Project at a glance

What does a medium-voltage submersible pump cable replacement involve?

A medium-voltage submersible pump cable replacement is a new cable built to the core functions and voltage rating the pump needs and to a diameter its cable entry accepts, so that it connects to the same motor, earth and control circuits and seals in the same cable entry. For this 6000 V pump in Kazakhstan the order specified three 50 mm² power cores, two earth cores, a screened control element for the pump's monitoring or control circuits, a 6/10 kV rating and a maximum outside diameter of 54 mm.

The pump runs on a variable-frequency drive, so the cable carries more than mains-frequency power. The drive's fast switching pulses travel down the 180 m run and reflect at the motor, which is why a du/dt filter sits at the drive output, and the pump's monitoring or control signals share the cable with those power cores. The overall tinned copper braid and the common braid over the two control pairs are there for that combination. The same construction is listed as a product, with its preliminary design values, on the (N)TSCGEWCUEUS 6/10 kV pump power and control cable page.

Reading the existing cable: power cores, earth conductors and a control element

Photographs of the existing cable on this 6000 V submersible pump, taken by the customer, show the arrangement the TEBAOFLEX replacement had to match. The existing cable has three medium-voltage power cores terminated with cable lugs, two green-yellow earth conductors and a white core printed CONTROL ELEMENT that carries the control wires, all under a black inner sheath, a copper wire braid and a red outer sheath. The replacement keeps the same core functions in the same kind of construction.

One difference shows at the termination. At the existing termination the earth connections are made with green-yellow conductors. In the (N)TSCGEWCUEUS construction the two 12.5 mm² earth cores are covered with semi-conductive rubber, so they appear black when the inner sheath is opened; the installer should allow for that when preparing the new cable ends.

Construction of the 6/10 kV replacement cable, layer by layer

The (N)TSCGEWCUEUS 6/10 kV replacement cable has three 50 mm² flexible tinned copper power cores, each with a semi-conductive conductor screen, EPR insulation and a semi-conductive insulation screen. Beside them sit two 12.5 mm² tinned copper earth cores covered with semi-conductive rubber and a control element of two twisted pairs of 0.5 mm² cores under one common tinned copper braid. A GM1b inner sheath, an overall tinned copper wire braid and a red 5GM5 polychloroprene outer sheath complete the cable.

1. Power conductor: flexible tinned copper, finely stranded, 50 mm² (three cores)
2. Conductor screen: semi-conductive compound over the conductor
3. Insulation: EPR rubber compound
4. Insulation screen: semi-conductive layer with a semi-conductive tape wrap
5. Earth core: tinned copper, 12.5 mm², covered with semi-conductive rubber (two cores, 25 mm² together)
6. Control element S(4×0.5): four 0.5 mm² tinned copper cores with EPR insulation as two twisted pairs under one common tinned copper wire braid
7. Inner sheath: GM1b-type rubber compound
8. Overall screen: tinned copper wire braid
9. Outer sheath: 5GM5-type polychloroprene (PCP) rubber, red

(N) in front of the designation marks a construction built with reference to the DIN VDE 0250 series, here DIN VDE 0250-813; it is not a VDE certification mark. The letters of designations like this one are explained, as far as the VDE legend defines them, in our guide to reading VDE cable designations.

What does S3×50+2×25/2+S(4×0.5) mean on this pump cable?

S3×50+2×25/2+S(4×0.5) lists the cores of the cable: S3×50 is the three 50 mm² power cores, 2×25/2 is a 25 mm² earth conductor divided into two 12.5 mm² cores, and S(4×0.5) is a screened control element of four 0.5 mm² cores. The buyer of this Kazakhstan order asked TEBAOFLEX to confirm the earth and control parts, and TEBAOFLEX confirmed that the two earth cores are 12.5 mm² each, 25 mm² together, and that the four control cores form two twisted pairs under a common tinned copper screen.

The same control element is sometimes written S(2×2×0.5), which states the two pairs directly; both forms appear in the correspondence for this order. Splitting the earth conductor into two cores lets them sit in the gaps between the round power cores, which keeps the cable round and flexible. Twisting each control pair and screening the pair group reduces the noise coupled into the control signals from the power cores next to them, which matters most on a VFD-fed pump.

Why EPR insulation and a polychloroprene sheath for a submersible pump cable

The parameter sheet for this (N)TSCGEWCUEUS 6/10 kV order specifies EPR insulation with semi-conductive rubber screens, a GM1b rubber inner sheath and a red 5GM5 polychloroprene (PCP) outer sheath. EPR gives high dielectric strength and stable performance in wet service, and the sheet describes the PCP sheath as resistant to water, oil, ozone, ultraviolet light, abrasion and tearing. The tin coating protects the copper conductors against oxidation and corrosion in water and keeps crimped and soldered terminations reliable.

The same sheet names IEC 60332-1-2 for flame propagation, IEC 60811-404 for oil resistance and IEC 60811-403 for ozone resistance as test references, and it states that the cable is not halogen-free, because the outer sheath is a polychloroprene compound. A station that needs halogen-free cable needs a different sheath, and the enquiry should say so. Why flexible cables use EPR rather than XLPE insulation is explained in our EPR insulation guide.

Will the replacement cable fit the pump's cable entry? The 54 mm limit

The 6/10 kV replacement cable for this 6000 V submersible pump had to seal in the pump's existing cable entry, so the buyer set a maximum outside diameter of 54 mm. The order's parameter sheet for this (N)TSCGEWCUEUS 6/10 kV cable gave a calculated range of 54–58 mm. The buyer asked whether a maximum of 54 mm could be confirmed, or which cable-entry grommet a larger cable would need, and TEBAOFLEX confirmed a finished diameter of no more than 54 mm as a factory acceptance test item.

A cable-entry seal grips the cable sheath over a narrow range of diameters. A cable that is too thick will not pass through the grommet; one that is too thin may not seal. That is why the diameter was agreed before the order as a 54 mm maximum and made a factory acceptance test item rather than left as a nominal value; whether the entry seals on the delivered cable is for the pump owner and its installer to confirm.

Can a 6 kV submersible pump on a VFD run through 180 m of this cable?

For a 6000 V submersible pump motor on a medium-voltage VFD with a du/dt filter, the voltage rating of this (N)TSCGEWCUEUS 6/10 kV cable (U₀/U 6/10 kV, Um 12 kV) covers the motor circuit: its conductor-to-earth rating U₀ equals the full 6 kV line voltage. Whether the drive, filter and motor work together over 180 m is the drive supplier's calculation. For that check TEBAOFLEX gave the buyer the cable's capacitance, 0.345 µF/km, and inductance, 0.371 mH/km; over the 180 m run these work out at about 0.062 µF and 0.067 mH.

When it is bonded all round at both the drive end and the pump end, the overall tinned copper braid gives the drive's high-frequency currents a low-impedance return path inside the cable, and the common braid over the control pairs reduces the noise coupled into the control circuit. What braid coverage means, and how braided and spiral screens compare, is explained in our spiral shield vs braided shield guide. The 200 A figure is a 30 °C free-air reference only and must be corrected for the actual route.

Why the order called for one continuous 180 m length without joints

The Kazakhstan order for this 6/10 kV submersible pump cable called for the 180 m as one continuous length on one drum, without joints, factory splices or repaired sections. In a medium-voltage pump cable that can lie in water, a joint is a point where water can enter and the insulation can fail. TEBAOFLEX confirmed the 180 m as all-new cable in one length and offered a letter confirming that it contains no joints.

Factory tests support that statement but cannot prove it on their own. A power conductor or screen broken right through would fail the conductor resistance or screen continuity check, and insulation damaged badly enough to break down, or to discharge above 10 pC at 1.73 U₀, would fail the voltage or partial discharge test. A well-made repair could still pass those tests. TEBAOFLEX told the buyer that a video cannot practically follow 180 m of cable from the first metre to the last, so it offered the joint-free letter to go with the promised photographs and video of the cable and its metre marking, and with the test report.

Factory acceptance test for a 6/10 kV pump cable: the criteria agreed for this order

The factory acceptance test agreed for this 6/10 kV submersible pump cable covers partial discharge (10 pC or less at 1.73 U₀), a 17 kV AC voltage test for 5 minutes on the power cores, a water immersion test followed by the voltage test, and a 2 kV AC test for 5 minutes on the control element. It also covers continuity and resistance of the overall braid and the control-element screen, conductor resistance, the outside diameter, the sheath and metre marking and the length on the drum. TEBAOFLEX stated the criteria at the buyer's request, and the buyer listed the results it wanted to see.

The drum has shipped and a factory test report was made for it. This record lists the criteria agreed for the order rather than measured values, because they are what a buyer writes into a medium-voltage pump cable order and what the factory is then held to.

Water immersion: the order criterion and the routine test

The water immersion criterion TEBAOFLEX stated for this order is 24 hours in clean water followed by 17 kV AC for 5 minutes, with no breakdown or flashover. In TEBAOFLEX's routine production the insulated cores rest in the workshop for at least 16 hours after insulation and are then immersed in water for at least 1 hour before their AC voltage test. State the immersion time your specification requires in the enquiry, so that it is written into the test plan.

How screen continuity and resistance are checked

In TEBAOFLEX's usual method the outer layers are stripped back at both ends of the cable to expose the overall tinned copper braid and the braid of the control element. Each screen is connected into a loop through the full length and its continuity and resistance are measured; a measured resistance shows the screen is continuous from end to end. TEBAOFLEX told the buyer that the screen resistances would be reported as measured values rather than calculated ones, because a resistance calculated by theory for a braid is not precise.

Partial discharge at 1.73 U₀

Partial discharge is a localised electrical discharge that only partly bridges the insulation, typically in a gas-filled void, at a contaminant or protrusion, or at a gap between the insulation and a semi-conductive screen. Measured as apparent charge in picocoulombs (pC), it reveals defects that can pass a voltage withstand test but erode the insulation over years. IEC 60502-2, the IEC standard for medium-voltage cables in fixed installations, has a comparable routine partial discharge test on screened cores at 1.73 U₀ with a measuring sensitivity of 10 pC or better. For this flexible pump cable, the 10 pC level at 1.73 U₀ is a criterion stated for the order, not a claim of compliance with IEC 60502-2. TEBAOFLEX measures it in a shielded test room, as documented with photographs in the 12/20 kV bucket-wheel excavator cable case.

What the buyer asked to see before accepting the drum

Before final acceptance of the 180 m drum of 6/10 kV pump cable, the buyer of this Kazakhstan order asked for the factory test report of the actual drum, photographs and video of the finished cable and drum, and photographs of the sheath and metre marking. It also asked for confirmation of the continuous joint-free length, the measured outside diameter, and the voltage, partial discharge, conductor resistance, screen continuity and water immersion results. TEBAOFLEX also offered a cross-section sample cut from the finished cable.

1. Test report for the actual drum, with measured values beside each criterion, not a type test from another cable.
2. Photographs and video of the finished cable and the drum, including the sheath print and metre marking.
3. Confirmation of the joint-free length; TEBAOFLEX offered a letter confirming it, since a video cannot follow all 180 m.
4. Measured outside diameter, against the 54 mm limit of the cable entry.
5. Cross-section sample of the finished cable, offered by TEBAOFLEX so the construction can be checked against the drawing.
6. A simple final cross-section drawing; the buyer did not ask for confidential manufacturing details.

TEBAOFLEX also invited the buyer to visit the factory and check the cable. A buyer who wants to witness the tests should say so in the enquiry, together with the documents required with the delivery.

Original pump cable or replacement cable: what the quotation should say

At the buyer's request, TEBAOFLEX agreed to describe this 6/10 kV cable in the quotation as a “replacement cable manufactured by Jiangsu TEBAOFLEX for the Xylem Flygt pump” and to state the exact designation, TEBAOFLEX (N)TSCGEWCUEUS 6/10 kV S3×50+2×25/2+S(4×0.5) mm². The buyer also asked for the quotation to be linked to the final approved data sheet and cross-section drawing. TEBAOFLEX is not the pump's original cable manufacturer.

That wording protects both sides. A purchase record worded this way shows a replacement cable from a named manufacturer, and linking the quotation to the approved data sheet and cross-section drawing, as the buyer asked, puts the technical approval on those documents and the agreed test criteria rather than on a part number. Where a pump also uses a monitoring system, the control cores have to be matched to it as well; how the original SUBCAB constructions compare for that check is covered on our Flygt SUBCAB MAS 800 cable review page.

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