Composition for heat cycle system, and heat cycle system

A composition for a heat cycle system, comprising:

• a working fluid containing trifluoroethylene and 2,3,3,3-tetrafluoropropene as unsaturated fluorinated hydrocarbon compounds, and optionally at least one other unsaturated fluorinated hydrocarbon compound containing at least one carbon-carbon unsaturated bond and represented by formula (I):
• CxFyRz (I)
• wherein R is H or Cl, x is an integer of from 2 to 6, y is an integer of from 1 to 12, and z is an integer of from 0 to 11, provided that 2x≥y+z≥2, and
• a refrigerant oil having a breakdown voltage of at least 25 kV, a hydroxyl value of at most 0.1 mgKOH/g, and a kinematic viscosity at 40° C. of from 5 to 200 mm2/s and a kinematic viscosity at 100° C. of from 1 to 100 mm2/s.

A composition for a heat cycle system, comprising:

• a working fluid containing difluoromethane as a saturated fluorinated hydrocarbon compound, trifluoroethylene as an unsaturated fluorinated hydrocarbon compound, and optionally at least one other unsaturated fluorinated hydrocarbon compound containing at least one carbon-carbon unsaturated bond and represented by formula (I):
• CxFyRz (I)
• wherein R is H or Cl, x is an integer of from 2 to 6, y is an integer of from 1 to 12, and z is an integer of from 0 to 11, provided that 2x≥y+z≥2;
• and
• a refrigerant oil having a breakdown voltage of at least 25 kV, a hydroxyl value of at most 0.1 mgKOH/g, and a kinematic viscosity at 40° C. of from 5 to 200 mm2/s and a kinematic viscosity at 100° C. of from 1 to 100 mm2/s.