1. A ground fault sensing device for a drive system that converts direct current electrical power from a direct current power supply into alternating current electrical power and drives an electric motor with that alternating current electrical power, comprising:
an extraction circuit that is connected to a power supply line of the direct current power supply via a coupling capacitor, that detects an amplitude wave that is generated when an alternating current side including the electric motor is suffering a ground fault, and that extracts the envelope of the amplitude wave;
a measurement circuit that measures the voltage level of the envelope; and
a determination circuit that makes a decision as to whether or not a ground fault has occurred on the alternating current side by comparing together the voltage level measured by the measurement circuit and a ground fault decision value.
2. A ground fault sensing device according to claim 1, wherein:
the determination circuit compares the difference between the voltage level measured by the measurement circuit and a reference voltage level set in advance with the ground fault decision value.
3. A ground fault sensing device according to claim 1, further comprising:
a test signal output circuit that applies a ground fault testing signal having a periodic waveform to the power supply line of the direct current power supply via the coupling capacitor; and
a direct current side ground fault sensing circuit that detects the response waveform when the ground fault testing signal is applied, and that detects the occurrence of a ground fault on the direct current side including the direct current power supply, on the basis of change of the response waveform, wherein:
the extraction circuit extracts the envelope of the amplitude wave superimposed upon the ground fault testing signal.
4. A ground fault sensing device according to claim 3, wherein:
the direct current side ground fault sensing circuit determines that a ground fault has occurred on the direct current side, if the value of the amplitude of the response waveform having a periodic waveform is smaller than an amplitude value set in advance that corresponds to a ground fault.
5. A ground fault sensing device according to claim 3, further comprising:
a control means that performs control so that ground fault sensing for the direct current side is performed with the direct current side ground fault sensing circuit, when the electric motor is stopped, and that performs control so that ground fault sensing for the alternating current side is performed by performing extraction with the extraction circuit, performing measurement with the measurement circuit, and performing determination with the determination circuit, when the electric motor is operating.
6. A ground fault sensing device according to claim 5, wherein:
the control means outputs a command to stop the drive system, when a ground fault on at least one of the alternating current side and the direct current side is detected.
7. A ground fault sensing device according to claim 1, wherein:
the ground fault decision value is set according to the rotation speed of the electric motor.
8. A ground fault sensing device according to claim 1, wherein:
the extraction circuit is an envelope detection circuit.
9. A ground fault sensing device according to claim 1, wherein:
the extraction circuit is a full wave rectification circuit.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An impact resistant acrylic polymer pellet comprising an acrylic multi-layer polymer having at least one rubber-like elastomer layer () as an inner layer and having a rigid polymer layer () as an outermost layer which is containing methyl methacrylate as a main component, wherein the proportion of parts insoluble in acetone including the polymer of the rubber-like elastomer layer () is from 70 to 97% by weight per unit weight of the pellet.
2. The impact resistant acrylic polymer pellet according to claim 1, wherein the proportion of the rubber-like elastomer is from 50 to 90% by weight per unit weight of the pellet.
3. The impact resistant acrylic polymer pellet according to claim 1, wherein the polymer constituting the rubber-like elastomer layer () is a polymer which shows a glass transition temperature of 25 C. or less in the case of homopolymerization; and the polymer constituting the rigid polymer layer () is a polymer which shows a glass transition temperature of 50 C. or more in the case of homopolymerization.
4. The impact resistant acrylic polymer pellet according to claim 1, wherein the rubber-like elastomer layer () is constituted from a polymer obtained by polymerizing 100 parts by weight of a monomer mixture composed of 40 to 90% by weight of an alkyl acrylate having an alkyl group of 8 or less carbon atoms and 10 to 60% by weight of a monofunctional monomer having one vinyl group which can be copolymerized with the alkyl acrylate, 0.1 to 10 parts by weight of a graft-linking agent, and 0.1 to 10 parts by weight of a multifunctional cross-linking agent having at least two vinyl groups; and the rigid polymer layer () is constituted from a polymer obtained by polymerizing a monomer or monomer mixture composed of 60 to 100% by weight of an alkyl methacrylate having an alkyl group of 4 or less carbon atoms and 0 to 40% by weight of an unsaturated monomer which can be copolymerized with the alkyl methacrylate.
5. The impact resistant acrylic polymer pellet according to claim 1, wherein the proportion of the ridid polymer layer () in the acrylic multi-layer polymer is from 10 to 50% by weight.
6. A method for producing the impact resistant acrylic polymer pellet of the claim 1, comprising:
a step of feeding a water-containing polymer (X) or a mixture of a water-containing polymer (X) with at least one organic stabilizer (Y) to a compression dehydration extruder,
wherein said water-containing polymer (X) is a polymer obtained by coagulating the emulsified latex of an acrylic multi-layer polymer containing a rubber-like elastomer, and is able to provide an acrylic multi-layer polymer which contains 40% by weight or less of fine powders having particle size of 212 m or less after drying and shows a volume of voids having pore size is 5 m or less being 0.7 ml or less per one gram of dired polymer measured by a mercury pressure method after drying,
said organic stabilizer (Y) is selected from the group consisting of a phosphorus-based compound, a hindered phenol-based compound and a hindered amine-based compound, and
said compression dehydration extruder comprises a dehydration part having at least one dehydration slit, a compression part for removing liquid substances from the water-containing polymer (X) and a deaeration part for discharging vaporized substances; and,
steps of dehydrating, drying, melting and extruding the water-containing polymer (X) or the mixture to form the pellet.
7. The method according to claim 6, wherein the amount of water discharged in a first dehydration part of the compression dehydration extruder is 55% or more based on the amount of water contained in the water-containing polymer (X).
8. The method according to claim 6, wherein the maximum resin temperature in the compression dehydration extruder is from 200 C. to 300 C.
9. The method according to claim 6, wherein the amount of alkaline earth metals derived from coagulation of the emulsified latex of the acrylic multi-layer polymer is 700 ppm or less.
10. The method according to claim 6, wherein the emulsified latex of the acrylic multi-layer polymer is poured at a linear speed of 0.5 ms or less into a coagulating agent solution of 1.8 to 5.0% aqueous calcium acetate solution at a temperature of 90 C. or more to be coagulated, and the resulted slurry is washed with distilled water in amount of 5-times by weight or more per weight of the polymer, then it is dehydrated to produce a water-containing polymer (X).