{"id":157,"date":"2026-07-08T08:50:52","date_gmt":"2026-07-08T08:50:52","guid":{"rendered":"https:\/\/industrialelectricmotor.net\/?p=157"},"modified":"2026-07-08T08:50:52","modified_gmt":"2026-07-08T08:50:52","slug":"what-is-a-vfd-motor","status":"publish","type":"post","link":"https:\/\/industrialelectricmotor.net\/fi\/what-is-a-vfd-motor\/","title":{"rendered":"What Is a VFD Motor"},"content":{"rendered":"
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Korea Ever-Power \u00b7 VFD Motor Guide \u00b7 IEC 60034-17<\/span><\/p>\n

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What Is a VFD Motor?
\nVariable Frequency Drive Motor Guide<\/span><\/h1>\n

A VFD motor, also called an inverter-duty motor or variable speed motor, is a three-phase induction motor specifically engineered to operate reliably across a wide speed range when driven by a variable frequency drive (VFD). Standard motors can fail prematurely on VFD supply due to voltage spike insulation damage, reduced cooling at low speed, and bearing current damage. A VFD motor addresses each of these mechanisms through specific design features not found in standard catalogue motors.<\/p>\n

Reinforced Winding Insulation<\/span>
\nIC416 External Blower<\/span>
\nPTC Thermistors<\/span>
\nInsulated Bearings<\/span>
\n10:1 Speed Range<\/span><\/div>\n<\/div>\n<\/div>\n

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10:1<\/div>\n
Constant torque speed range (IC416 blower)<\/div>\n<\/div>\n
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1.35 kV<\/div>\n
Impulse voltage withstand (reinforced insulation)<\/div>\n<\/div>\n
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30\u201350%<\/div>\n
Energy saving vs fixed-speed fan\/pump<\/div>\n<\/div>\n
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Class H<\/div>\n
Insulation class (180\u00b0C rated)<\/div>\n<\/div>\n
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0\u2013120 Hz<\/div>\n
Operating frequency range<\/div>\n<\/div>\n<\/div>\n

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\"VFD<\/p>\n
Korea Ever-Power YVF2 series VFD motor \u2014 the IC416 forced ventilation blower on the non-drive end maintains rated cooling airflow at all speeds from 0 to rated, enabling full torque operation across the 10:1 constant torque speed range without thermal derating.<\/div>\n<\/div>\n

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Contents<\/div>\n
1. Why a Standard Motor Fails on VFD Supply<\/a>
\n2. VFD Motor Design Features Explained<\/a>
\n3. Cooling at Variable Speed: IC411 vs IC416<\/a>
\n4. Bearing Current and How to Prevent It<\/a>
\n5. VFD Energy Saving Calculations<\/a>
\n6. Korea Ever-Power YVF2 Series<\/a>
\n7. Frequently Asked Questions<\/a><\/div>\n<\/div>\n

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1. Why a Standard Motor Fails on VFD Supply<\/h2>\n

A variable frequency drive outputs a pulse-width modulated (PWM) voltage waveform rather than a pure sinusoidal supply. Although the fundamental frequency and average voltage can be accurately controlled to achieve variable speed, the rapid switching transitions in the PWM waveform create voltage spikes that can reach 2 to 3 times the supply voltage at the motor terminals when the cable length between drive and motor exceeds a few metres. These voltage spikes stress the winding insulation in ways that standard motor insulation systems were not designed to withstand.<\/p>\n

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Insulation Turn-to-Turn Failure<\/div>\n

PWM voltage spikes can reach 1,200 V or more at the motor terminals on a 380 V drive system. Standard motor winding insulation is tested to approximately 1,000 V and will degrade from repetitive exposure to these spikes. The failure typically begins at the first coil turn, which receives the full voltage spike before the wavefront is attenuated along the winding. Over weeks to months, partial discharge damages the turn-to-turn insulation, eventually causing a winding short circuit.<\/p>\n<\/div>\n

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Thermal Overload at Low Speed<\/div>\n

A standard IC411 (TEFC) motor relies on its shaft-mounted fan to circulate cooling air over the frame. At low speed under VFD control, the fan turns slowly and delivers far less cooling airflow. At 25 percent of rated speed (for example, 360 rpm on a 4-pole motor), the cooling fan delivers approximately 6 percent of rated airflow (proportional to speed). The motor winding losses remain high at full torque, but cooling capacity is almost absent \u2014 causing rapid overheating if the motor runs at full torque at low speed.<\/p>\n<\/div>\n

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Bearing Electrical Erosion<\/div>\n

PWM switching creates common-mode voltages on the motor shaft relative to earth. When the shaft voltage exceeds the lubricant film dielectric breakdown voltage in the bearing, a discharge current flows through the bearing ball-to-race contact. Repeated discharges erode the bearing raceway surface, producing a characteristic frosted or fluted appearance. The bearing becomes progressively noisier and fails prematurely \u2014 typically in 6 to 18 months compared to 20,000+ hours on sinusoidal supply.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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2. VFD Motor Design Features Explained<\/h2>\n

A VFD motor, such as Korea Ever-Power\u2019s YVF2 series, incorporates specific engineering modifications to address each of the three failure mechanisms described above. These features make the motor suitable for continuous operation at any speed within the rated range without accelerated ageing.<\/p>\n

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Reinforced Winding Insulation<\/div>\n

VFD motors use Class H insulation (180\u00b0C rated) with corona-resistant enamelled wire for the stator winding. The corona-resistant (CR) wire has an additional coating that resists partial discharge at voltage levels above the insulation threshold. The slot liner material is upgraded from standard polyester to an aramid-based material with higher dielectric strength. The winding impregnation uses a VPI (vacuum pressure impregnation) resin system that eliminates voids in the coil insulation where partial discharge could initiate. Together, these measures raise the effective impulse voltage withstand of the winding from approximately 1,000 V (standard) to 1,350 V or higher, well above the peak VFD spike voltage on a 380 V system.<\/p>\n

IEC 60034-17 and IEC 60034-25 define the impulse voltage test requirements for inverter-duty motors<\/div>\n<\/div>\n
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IC416 Forced Ventilation Blower<\/div>\n

The IC416 cooling system replaces the shaft-mounted fan (IC411) with a separately powered external blower motor mounted on the non-drive end of the main motor. The blower runs at fixed speed continuously, independent of the main motor shaft speed, maintaining rated cooling airflow even when the main motor runs at near-zero speed. This allows the VFD motor to deliver full rated torque from 0 rpm to rated speed \u2014 the 10:1 constant torque speed range \u2014 without any thermal derating. Korea Ever-Power YVF2 series blower motors are rated 380 V 50 Hz three-phase, typically 50 to 250 W depending on the main motor frame size.<\/p>\n

IC416 = independent motor-driven external blower; IC411 = shaft-mounted internal fan<\/div>\n<\/div>\n
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PTC Thermistors<\/div>\n

Korea Ever-Power YVF2 series motors include PTC (Positive Temperature Coefficient) thermistor sensors embedded in the stator winding at the hottest point of each phase. PTC thermistors have a sharp resistance increase at a defined trip temperature (typically 130\u00b0C or 150\u00b0C). The thermistors connect to a PTC relay module in the VFD control panel, which trips the drive if any winding reaches the set temperature. This provides direct winding temperature protection independent of the external thermal overload relay, which only monitors motor current and cannot directly detect winding overtemperature caused by cooling system failure or excessive ambient temperature.<\/p>\n<\/div>\n

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Insulated Bearings (NDE)<\/div>\n

To interrupt the bearing current discharge path, YVF2 series motors above 75 kW are fitted with an insulated bearing sleeve in the non-drive-end bearing housing. The sleeve provides electrical isolation between the bearing outer ring and the motor end shield, preventing common-mode shaft voltage from completing a circuit through the NDE bearing. The drive-end bearing remains uninsulated to provide the required earth reference. An earthing brush (shaft grounding brush) may also be specified for very long cable runs or sensitive drive configurations where NDE bearing insulation alone is insufficient.<\/p>\n<\/div>\n<\/div>\n<\/div>\n

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3. Cooling at Variable Speed: IC411 vs IC416<\/h2>\n
\n\n\n\n\n\n\n\n\n\n\n
Property<\/th>\nIC411 (Standard TEFC)<\/th>\nIC416 (VFD Motor Blower)<\/th>\n<\/tr>\n<\/thead>\n
Cooling airflow source<\/td>\nShaft-mounted fan, speed proportional to motor shaft<\/td>\nSeparate constant-speed blower motor, independent of main shaft<\/td>\n<\/tr>\n
Cooling at 10% speed<\/td>\n~0.1% of rated cooling capacity<\/td>\n100% of rated cooling capacity<\/td>\n<\/tr>\n
Constant torque speed range<\/td>\nTypically 50\u2013100% of rated speed (2:1 or less)<\/td>\n0\u2013100% of rated speed (10:1 or greater)<\/td>\n<\/tr>\n
Additional supply needed<\/td>\nNone<\/td>\n380 V three-phase for blower motor (50\u2013250 W)<\/td>\n<\/tr>\n
Noise level at low speed<\/td>\nReduced (fan turns slowly)<\/td>\nConstant blower noise regardless of motor speed<\/td>\n<\/tr>\n
Typical applications<\/td>\nVariable torque loads (fans, pumps) with speed range above 50% rated<\/td>\nConstant torque loads at wide speed range: extruders, conveyors, machine tools, hoists<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
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Note for centrifugal fan and pump drives: for variable torque loads where speed rarely drops below 50 percent of rated, a standard motor with IC411 cooling may be adequate for VFD use because the centrifugal load naturally reduces torque at reduced speed, keeping winding temperatures manageable even with reduced fan cooling. However, the winding insulation reinforcement is still required regardless of the load type to protect against PWM voltage spikes.<\/p>\n<\/div>\n<\/div>\n

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4. Bearing Current and How to Prevent It<\/h2>\n

Bearing current damage is one of the most insidious failure modes in VFD-driven motors because it produces no immediate symptoms. The motor runs normally, with normal current and temperature, but the bearings are being progressively damaged by microscopic electrical discharges. The first symptom is typically an audible roughness in bearing rotation, by which time raceway fluting (a regular pattern of circumferential grooves on the bearing inner or outer race) is already established and bearing replacement is necessary.<\/p>\n

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Bearing Current Prevention Methods<\/div>\n
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Insulated NDE Bearing<\/div>\n

Ceramic coating on bearing outer ring or insulated bearing sleeve in end shield. Breaks the discharge circuit at the NDE bearing. Standard on YVF2 above 75 kW. Most cost-effective solution for motors above 75 kW.<\/p>\n<\/div>\n

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Shaft Grounding Brush<\/div>\n

Carbon or silver-loaded brush rides on motor shaft, providing a low-impedance path to earth for common-mode shaft voltage. Discharges shaft voltage to earth before it can build to bearing lubricant breakdown level. Effective on all motor sizes; requires periodic brush replacement.<\/p>\n<\/div>\n

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Output Dv\/dt Filter<\/div>\n

LC filter installed between VFD output and motor cable limits the voltage rise rate of PWM pulses at the motor terminals. Reduces peak voltage spike amplitude and slows the voltage wavefront, reducing both insulation stress and common-mode current magnitude. Recommended for cable runs above 50 metres.<\/p>\n<\/div>\n

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Common-Mode Choke<\/div>\n

Toroidal inductor on the drive output cable attenuates the common-mode current that creates shaft voltage. Often used in combination with a shaft grounding brush or NDE insulated bearing for comprehensive bearing current protection on large motors with long cable runs.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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5. VFD Energy Saving Calculations<\/h2>\n

For centrifugal fan and pump loads, reducing motor speed with a VFD produces disproportionately large energy savings because power demand follows the cube law: power is proportional to the cube of speed. A 20 percent speed reduction yields a 49 percent power reduction.<\/p>\n

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Worked Example \u2014 22 kW Centrifugal Pump, Operating at 80% Flow Demand<\/div>\n
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Fixed speed (throttle valve control)<\/div>\n
22.0 kW<\/div>\n
Motor runs at full speed; flow controlled by valve restriction<\/div>\n<\/div>\n
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VFD at 80% speed (92.8% flow)<\/div>\n
11.3 kW<\/div>\n
Power = 22 \u00d7 (0.8)\u00b3 = 22 \u00d7 0.512 = 11.3 kW<\/div>\n<\/div>\n
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Annual saving (8,000 h\/yr, 0.12 USD\/kWh)<\/div>\n
10,300 USD<\/div>\n
(22.0 \u2212 11.3) \u00d7 8,000 \u00d7 0.12 = 10,272 USD\/year<\/div>\n<\/div>\n
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Typical VFD + YVF2 motor cost<\/div>\n
~4,500 USD<\/div>\n
Simple payback: ~5 months at this operating profile<\/div>\n<\/div>\n<\/div>\n<\/div>\n

This calculation assumes the system operates at 80% of maximum flow for most of the year. In practice, process flow demand varies, and the energy saving at partial flow is even greater than this example shows. VFD installation on centrifugal pump and fan applications typically achieves payback in 6 to 18 months at typical industrial electricity prices, making it one of the most financially attractive energy efficiency investments available to process plant operators.<\/p>\n<\/div>\n

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6. Korea Ever-Power YVF2 Series VFD Motor<\/h2>\n
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The YVF2 series is Korea Ever-Power\u2019s inverter-duty motor range, designed for VFD variable speed applications across industrial drives. The full range is detailed in the VFD inverter-duty motor product section<\/a>, covering 0.75 kW to 200 kW in IEC frame sizes 80M through 315M in 4-pole configuration, with 2-pole and 6-pole variants available on request.<\/p>\n

All YVF2 motors are built to IE3 efficiency (measured at 50 Hz sinusoidal supply per IEC 60034-30-1). The IC416 external blower enables full rated torque from 0 to 50 Hz (0 to 1,450 rpm for 4-pole) with no derating, and continued operation above 50 Hz up to 120 Hz (up to 3,500 rpm) with constant power characteristic above base speed. This wide operating range covers extruder drives, conveyor speed control, machine tool axis drives, and large fan and pump installations with long daily operating hours.<\/p>\n<\/div>\n

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YVF2 Series Key Specifications<\/div>\n\n\n\n\n\n\n\n\n\n\n\n
Power range<\/td>\n0.75 \u2013 200 kW<\/td>\n<\/tr>\n
Voltage<\/td>\n380 V \u00b1 5%, 50 Hz<\/td>\n<\/tr>\n
Frequency range<\/td>\n0 \u2013 120 Hz<\/td>\n<\/tr>\n
Cooling<\/td>\nIC416 external blower<\/td>\n<\/tr>\n
Constant torque range<\/td>\n10:1 (0 \u2013 50 Hz)<\/td>\n<\/tr>\n
Insulation<\/td>\nClass H, CR wire<\/td>\n<\/tr>\n
Protection<\/td>\nIP54 (IP55 on request)<\/td>\n<\/tr>\n
Thermistors<\/td>\nPTC, 3 per motor<\/td>\n<\/tr>\n
NDE bearing (\u226575 kW)<\/td>\nInsulated sleeve standard<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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\"VFD<\/p>\n

Pump and HVAC<\/div>\n<\/div>\n
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\"VFD<\/p>\n

Printing Drives<\/div>\n<\/div>\n
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\"Korea<\/p>\n

Rotor Production<\/div>\n<\/div>\n
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\"Korea<\/p>\n

CE and ISO Certified<\/div>\n<\/div>\n<\/div>\n

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7. Frequently Asked Questions<\/h2>\n
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Can I use a standard motor on a VFD for a fan application?<\/div>\n<\/div>\n
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For centrifugal fan applications where the minimum required speed is above 50 percent of rated speed, a standard motor with reinforced insulation may be acceptable, provided the winding insulation upgrade is confirmed with the motor supplier. At 50 percent speed, cooling airflow from the shaft-mounted fan is approximately 12.5 percent of rated \u2014 but the centrifugal load torque at 50 percent speed is only 25 percent of rated, so winding losses are also reduced. However, a properly specified VFD motor (IC416 blower, Class H insulation, PTC thermistors) is always the correct specification for new installations where operating life and maintenance cost are important, even for variable torque applications.<\/p>\n<\/div>\n<\/div>\n

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What VFD parameters should I set when commissioning a YVF2 motor?<\/div>\n<\/div>\n
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For initial commissioning of Korea Ever-Power YVF2 series motors on a VFD, set the following parameters as a starting point: rated motor voltage (380 V), rated frequency (50 Hz), rated current (per nameplate), motor power factor (per nameplate). Enable PTC thermistor input and connect the motor PTC leads to the VFD PTC input terminals. Set acceleration time to 10 to 30 seconds for conveyor and pump loads (longer for high-inertia loads). Set minimum frequency to 3 Hz (not 0 Hz) to prevent thermal overload at near-zero speed unless the application specifically requires holding torque at standstill. Set the carrier frequency (switching frequency) to 2 to 4 kHz for the first commissioning run \u2014 higher carrier frequencies reduce audible noise but increase common-mode currents and bearing current risk.<\/p>\n<\/div>\n<\/div>\n

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What is the difference between open-loop and closed-loop VFD control for a YVF2 motor?<\/div>\n<\/div>\n
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Open-loop (V\/f) control is the simplest VFD operating mode: the drive maintains a constant voltage-to-frequency ratio and outputs a set frequency corresponding to the demanded speed. The actual motor speed depends on slip and will vary slightly with load changes. Accuracy: typically \u00b12 to 5 percent of set speed. Suitable for pumps, fans, compressors, and conveyors where exact speed accuracy is not critical. Closed-loop vector control uses a shaft encoder or resolver to measure the actual rotor position and speed, allowing the VFD to calculate and apply the exact current vector needed for the demanded torque at any speed. Accuracy: typically \u00b10.01 percent of rated speed. Required for machine tool axis drives, winding tension control, and precise conveyor synchronisation applications. Korea Ever-Power YVF2 motors are compatible with both operating modes; encoder mounting brackets are available for closed-loop installations.<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n

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Korea Ever-Power \u00b7 YVF2 Series VFD Motors<\/div>\n

Need a VFD Motor for Your Variable Speed Application?<\/h2>\n

Korea Ever-Power YVF2 series: IC416 blower cooling, Class H insulation, PTC thermistors, insulated NDE bearings on motors above 75 kW. Available 0.75 to 200 kW from stock.<\/p>\n

View YVF2 VFD Motors<\/a><\/p>\n<\/div>\n<\/div>\n

Edited by Cxm<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"

Korea Ever-Power \u00b7 VFD Motor Guide \u00b7 IEC 60034-17 What Is a VFD Motor? Variable Frequency Drive Motor Guide A VFD motor, also called an inverter-duty motor or variable speed motor, is a three-phase induction motor specifically engineered to operate reliably across a wide speed range when driven by a variable frequency drive (VFD). Standard […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[28],"tags":[],"class_list":["post-157","post","type-post","status-publish","format-standard","hentry","category-industrial-electric-motor"],"_links":{"self":[{"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/posts\/157","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/comments?post=157"}],"version-history":[{"count":1,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/posts\/157\/revisions"}],"predecessor-version":[{"id":159,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/posts\/157\/revisions\/159"}],"wp:attachment":[{"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/media?parent=157"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/categories?post=157"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/industrialelectricmotor.net\/fi\/wp-json\/wp\/v2\/tags?post=157"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}